Removed FIXME comment

[radarhere]

PR #2544 resolved the immediate problem of #2563, but it also added a comment.

Pillow/setup.py

Lines 684 to 687 in 943a7a8

	# FIXME (melvyn-sopacua):
	# At this point it's possible that best_path is already in
	# self.compiler.include_dirs. Should investigate how that is
	# possible.

The user was thinking about the logic of the hardcoded paths in setup.py and our use of pkg-config, but it is possible for any given path to be in self.compiler.include_dirs from the very beginning of build_extensions() if the user added it in their install command, like

python3 -m pip install . -v --global-option=build_ext --global-option="-Iinsertedpath"

If the user wants to be eager in adding include directories, I don't think that is a problem. So this PR removes the comment, as it is at least misleading.

[radarhere]

The 3.12 failures are fixed by PR #7059