[MINOR][BUILD] Fix javadoc8 break
## What changes were proposed in this pull request?
These error below seems caused by unidoc that does not understand double commented block.
```
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:69: error: class, interface, or enum expected
[error] * MapGroupsWithStateFunction<String, Integer, Integer, String> mappingFunction =
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:69: error: class, interface, or enum expected
[error] * MapGroupsWithStateFunction<String, Integer, Integer, String> mappingFunction =
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:70: error: class, interface, or enum expected
[error] * new MapGroupsWithStateFunction<String, Integer, Integer, String>() {
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:70: error: class, interface, or enum expected
[error] * new MapGroupsWithStateFunction<String, Integer, Integer, String>() {
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:72: error: illegal character: '#'
[error] * @Override
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:72: error: class, interface, or enum expected
[error] * @Override
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:73: error: class, interface, or enum expected
[error] * public String call(String key, Iterator<Integer> value, KeyedState<Integer> state) {
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:73: error: class, interface, or enum expected
[error] * public String call(String key, Iterator<Integer> value, KeyedState<Integer> state) {
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:73: error: class, interface, or enum expected
[error] * public String call(String key, Iterator<Integer> value, KeyedState<Integer> state) {
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:73: error: class, interface, or enum expected
[error] * public String call(String key, Iterator<Integer> value, KeyedState<Integer> state) {
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:73: error: class, interface, or enum expected
[error] * public String call(String key, Iterator<Integer> value, KeyedState<Integer> state) {
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:76: error: class, interface, or enum expected
[error] * boolean shouldRemove = ...; // Decide whether to remove the state
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:77: error: class, interface, or enum expected
[error] * if (shouldRemove) {
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:79: error: class, interface, or enum expected
[error] * } else {
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:81: error: class, interface, or enum expected
[error] * state.update(newState); // Set the new state
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:82: error: class, interface, or enum expected
[error] * }
[error] ^
[error] .../forked/spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:85: error: class, interface, or enum expected
[error] * state.update(initialState);
[error] ^
[error] .../forked/spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:86: error: class, interface, or enum expected
[error] * }
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:90: error: class, interface, or enum expected
[error] * </code></pre>
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:92: error: class, interface, or enum expected
[error] * tparam S User-defined type of the state to be stored for each key. Must be encodable into
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:93: error: class, interface, or enum expected
[error] * Spark SQL types (see {link Encoder} for more details).
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:94: error: class, interface, or enum expected
[error] * since 2.1.1
[error] ^
```
And another link seems unrecognisable.
```
.../spark/sql/core/target/java/org/apache/spark/sql/KeyedState.java:16: error: reference not found
[error] * That is, in every batch of the {link streaming.StreamingQuery StreamingQuery},
[error]
```
Note that this PR does not fix the two breaks as below:
```
[error] .../spark/sql/core/target/java/org/apache/spark/sql/DataFrameStatFunctions.java:43: error: unexpected content
[error] * see {link DataFrameStatsFunctions.approxQuantile(col:Str* approxQuantile} for
[error] ^
[error] .../spark/sql/core/target/java/org/apache/spark/sql/DataFrameStatFunctions.java:52: error: bad use of '>'
[error] * param relativeError The relative target precision to achieve (>= 0).
[error] ^
[error]
```
because these seem probably fixed soon in https://github.com/apache/spark/pull/16776 and I intended to avoid potential conflicts.
## How was this patch tested?
Manually via `jekyll build`
Author: hyukjinkwon <gurwls223@gmail.com>
Closes #16926 from HyukjinKwon/javadoc-break.
3b4376876f