TST: Remove test_apply_mutate.py

[rhshadrach]

• closes #xxxx (Replace xxxx with the GitHub issue number)
• Tests added and passed if fixing a bug or adding a new feature
• All code checks passed.
• Added type annotations to new arguments/methods/functions.
• Added an entry in the latest doc/source/whatsnew/vX.X.X.rst file if fixing a bug or adding a new feature.

[rhshadrach]

Removing this test, it is the same as:

pandas/pandas/tests/groupby/test_apply.py

Lines 230 to 247 in a8a84c8

	@pytest.mark.parametrize(
	"func",
	[
	lambda x: x,
	lambda x: x[:],
	lambda x: x.copy(deep=False),
	lambda x: x.copy(deep=True),
	],
	)
	def test_groupby_apply_identity_maybecopy_index_identical(func):
	# GH 14927
	# Whether the function returns a copy of the input data or not should not
	# have an impact on the index structure of the result since this is not
	# transparent to the user
	df = DataFrame({"g": [1, 2, 2, 2], "a": [1, 2, 3, 4], "b": [5, 6, 7, 8]})
	result = df.groupby("g", group_keys=False).apply(func)
	tm.assert_frame_equal(result, df[["a", "b"]])

[mroeschke]

Thanks @rhshadrach