docs: kernel_include.py: remove Include class inheritance

docs: kernel_include.py: remove Include class inheritance

While the original code came from the Sphinx Include class,
such class is monolithic: it has only one function that does
everything, and 3 variables that are used:

	- required_arguments
	- optional_arguments
	- option_spec

So, basically those are the only members that remain from
the original class, but hey! Those are the same vars that every
other Sphinx directive extension has to define!

In summary, keeping inheritance here doesn't make much sense.

Worse than that, kernel-include doesn't support the current set
of options that the original Include class has, but it also
has its own set of options.

So, let's fill in the argument vars with what it does
support, dropping the rest.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/a9f2eebf11c6b0c3a2e3bf42e71392cdfd2835d1.1755872208.git.mchehab+huawei@kernel.org