docs: extensions: don't use utf-8 syntax for descriptions

docs: extensions: don't use utf-8 syntax for descriptions

None of the descriptions at the Sphinx extensions are using
non-ascii characters, so no need to place them under u"""
notation.

Also, according with:
	https://docs.python.org/3/deprecations/pending-removal-in-3.16.html

the 'u' format code is scheduled to be removed in Python 3.16.

So, let's just use """.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Reviewed-by: Kees Cook <kees@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/8a42f6be53464af4b866492a7e9ddf29c0429997.1739254187.git.mchehab+huawei@kernel.org