[docs][scikit-learn] removed duplicated docstrings

[StrikerRUS]

Refer to sphinx-doc/sphinx#7817 (comment).

Completely remove attribute names from __init__ docstring because new Sphinx version doesn't fully comply with numpy docstring guide in terms of

Attributes that are properties and have their own docstrings can be simply listed by name:
https://numpydoc.readthedocs.io/en/latest/format.html#class-docstring

Ugly constructions like :obj: are needed to workaround pydocstyle test:

./python-package/lightgbm/sklearn.py:680 in public method `best_score_`:
        D401: First line should be in imperative mood; try rephrasing (found 'dict')
./python-package/lightgbm/sklearn.py:680 in public method `best_score_`:
        D403: First word of the first line should be properly capitalized ('Dict', not 'dict')
./python-package/lightgbm/sklearn.py:687 in public method `best_iteration_`:
        D403: First word of the first line should be properly capitalized ('Int', not 'int')
./python-package/lightgbm/sklearn.py:694 in public method `objective_`:
        D401: First line should be in imperative mood; try rephrasing (found 'string')
./python-package/lightgbm/sklearn.py:694 in public method `objective_`:
        D403: First word of the first line should be properly capitalized ('String', not 'string')
./python-package/lightgbm/sklearn.py:708 in public method `evals_result_`:
        D401: First line should be in imperative mood; try rephrasing (found 'dict')
./python-package/lightgbm/sklearn.py:708 in public method `evals_result_`:
        D403: First word of the first line should be properly capitalized ('Dict', not 'dict')
./python-package/lightgbm/sklearn.py:715 in public method `feature_importances_`:
        D205: 1 blank line required between summary line and description (found 0)
./python-package/lightgbm/sklearn.py:715 in public method `feature_importances_`:
        D400: First line should end with a period (not 's')
./python-package/lightgbm/sklearn.py:715 in public method `feature_importances_`:
        D403: First word of the first line should be properly capitalized ('Array', not 'array')
./python-package/lightgbm/sklearn.py:729 in public method `feature_name_`:
        D403: First word of the first line should be properly capitalized ('Array', not 'array')
./python-package/lightgbm/sklearn.py:891 in public method `classes_`:
        D403: First word of the first line should be properly capitalized ('Array', not 'array')

[jameslamb]

oy yeah it is annoying to have to use obj. But I think this is better than having a ceiling on Sphinx. Thanks!

[StrikerRUS]

@jameslamb @guolinke Seems that neither closing-reopening nor rebasing can eliminate obsolete GitHub Actions checks. Refer to #3065 (comment).

[jameslamb]

@jameslamb @guolinke Seems that neither closing-reopening nor rebasing can eliminate obsolete GitHub Actions checks. Refer to #3065 (comment).

unfortunately I can't see the settings to confirm, but it must be that those old "required" ones are still listed in the settings :/

[jameslamb]

by the way @StrikerRUS , I asked if it is possible to just say "All GitHub Actions must pass" so we don't have to keep dealing with this...it is not :/

https://gh.neting.ccmunity/t/is-it-possible-to-require-all-github-actions-tasks-to-pass-without-enumerating-them/117957

[github-actions]

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