[Minor] [ML] [PySpark] Cleanup test cases of clustering.py

[yanboliang]

Test cases should be removed from annotation of setXXX function, otherwise it will be parts of Python API docs.
cc @mengxr @jkbradley

[SparkQA]

Test build #50346 has finished for PR 10975 at commit 0e749a9.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[mengxr]

I don't have strong preference about whether this should live inside the doctest or not. But we need to have this test somewhere to make sure the default value is not changed by accident. @yanboliang Could you add them to the unit test file?

[yanboliang]

@mengxr I did not found other class has similar test except KMeans, is this deliberately designed or lacks of some test cases?

[SparkQA]

Test build #50471 has finished for PR 10975 at commit 926ef04.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[mengxr]

Not by design, we just don't have excellent test coverage ...

LGTM. Merged into master. Thanks!