scripts/kernel-doc: remove an obscure logic from kernel-doc

scripts/kernel-doc: remove an obscure logic from kernel-doc

Kernel-doc has an obscure logic that uses an external file
to map files via a .tmp_filelist.txt file stored at the current
directory. The rationale for such code predates git time,
as it was added on Kernel v2.4.5.5, with the following description:

	# 26/05/2001 -         Support for separate source and object trees.
	#              Return error code.
	#              Keith Owens <kaos@ocs.com.au>

from commit 396a6123577d ("v2.4.5.4 -> v2.4.5.5") at the historic
tree:
	https://git.kernel.org/pub/scm/linux/kernel/git/history/history.git/

Support for separate source and object trees is now done on a different
way via make O=<object>.

There's no logic to create such file, so it sounds to me that this is
just dead code.

So, drop it.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/fd3b28dec36ba1668325d6770d4c4754414337fc.1739340170.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>