maint: avoid patching help2man

maint: avoid patching help2man

Commit cde1ea0e separated the coreutils-specific patches from help2man.
Most changes had been made to accommodate to the coreutils style guide,
i.e., to avoid syntax-check failures like sc_long_lines.
Yet 2 changes had to be put into the patch help2man.diff.
But this added the dependency to patch(1) in distribution builds.
Incidentally, the 2 remaining parts of the patch can easily be
done outside of help2man.  Therefore, this commit partly reverts
the recent separation of help2man into 'help2man.in' and
'help2man.diff', and instead uses the original help2man script.

* man/help2man.in: Rename to ...
* man/help2man: ... this file.
* man/help2man.diff: Remove.
* man/local.mk (mandeps): Remove man/help2man.
(man/help2man): Remove recipe.
(.x.1): Add the --info-page option when calling help2man in order
to change the name of the texinfo manual from the default, "info PRG",
to "info coreutils 'PRG invocation'".
Furthermore, use an sed pattern to remove the sentence starting
with "For complete documentation".
* .gitignore (/man/help2man): Remove entry.
* .x-update-copyright: Replace the entries for the files
'man/help2man.diff' and 'man/help2man.in' by 'man/help2man'.
* cfg.mk (sc_long_lines): Instead of 'man/help2man.in', exempt
'man/help2man' from this test.
(sc_po_check): Likewise.
(sc_space_tab): Instead of 'man/help2man.diff', exempt 'man/help2man'
from this test.
(sc_trailing_blank): Likewise.
(sc_prohibit_tab_based_indentation): Instead of 'man/help2man.in' and
'man/help2man.diff', exempt 'man/help2man'.
* man/dummy-man: Recognize the option --info-page=... as no-op.