When bumping sphinx, remove FrameType workaround in docs/source/conf.py

[jakkdl]

github.com/sphinx-doc/sphinx/issues/11802
sphinx-doc/sphinx#11861
being fixed should make

trio/docs/source/conf.py

Lines 200 to 203 in d1cc062

	# `types.FrameType.__module__` is "builtins", so sphinx looks for
	# builtins.FrameType.
	# See https://github.com/sphinx-doc/sphinx/issues/11802
	add_mapping("class", "types", "FrameType")

redundant. Though I had some issues with getting TracebackType working with their workaround previously:

trio/src/trio/testing/_raises_group.py

Lines 22 to 24 in d1cc062

	# sphinx will *only* work if we use types.TracebackType, and import
	# *inside* TYPE_CHECKING. No other combination works.....
	import types

that'll probably be the case with FrameType as well - and if so we should probably investigate and open an issue in sphinx about it.