## What changes were proposed in this pull request?
some cleanup and tiny optimization
1, since the `transformImpl` method in the .mllib side is no longer used in the .ml side, the scope should be limited;
2, in the `hashUDF`, val `numOfFeatures` is never used;
3, in the udf, it is inefficient to involve param getter (`$(numFeatures)`/`$(binary)`) directly or via method `indexOf` ((`$(numFeatures)`) . instead, the getter should be called outside of the udf;
## How was this patch tested?
existing suites
Closes#25324 from zhengruifeng/hashingtf_cleanup.
Authored-by: zhengruifeng <ruifengz@foxmail.com>
Signed-off-by: Sean Owen <sean.owen@databricks.com>
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