DEPR: Remove old-style warnings Categorical init

[TomAugspurger]

See

pandas/pandas/core/categorical.py

Lines 319 to 332 in fdbc6b8

	# there were two ways if categories are present
	# - the old one, where each value is a int pointer to the levels
	# array -> not anymore possible, but code outside of pandas could
	# call us like that, so make some checks
	# - the new one, where each value is also in the categories array
	# (or np.nan)
	# make sure that we always have the same type here, no matter what
	# we get passed in
	categories = self._validate_categories(categories)
	codes = _get_codes_for_values(values, categories)
	# TODO: check for old style usage. These warnings should be removes
	# after 0.18/ in 2016

[toobaz]

Sorry, I had missed this, anyway it was just fixed in #18022