### What changes were proposed in this pull request?
jira link: https://issues.apache.org/jira/browse/SPARK-30930
Remove ML/MLLIB DeveloperApi annotations.
### Why are the changes needed?
The Developer APIs in ML/MLLIB have been there for a long time. They are stable now and are very unlikely to be changed or removed, so I unmark these Developer APIs in this PR.
### Does this PR introduce any user-facing change?
Yes. DeveloperApi annotations are removed from docs.
### How was this patch tested?
existing tests
Closes#27859 from huaxingao/spark-30930.
Authored-by: Huaxin Gao <huaxing@us.ibm.com>
Signed-off-by: Sean Owen <srowen@gmail.com>