docs: remove Sphinx 1.x compatibility code

In general, the Use_SSI workaround is no longer needed, and neither is
the pre-1.6 logging shim for kerneldoc.

Signed-off-by: John Snow <jsnow@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-id: 20240703175235.239004-3-jsnow@redhat.com
[rebased on top of origin/master. --js]
Signed-off-by: John Snow <jsnow@redhat.com>
4 files changed