man: drop optional qualifiers for file/modulename

man: drop optional qualifiers for file/modulename

Most tools don't consider the file/module name as optional, so we can
drop the square brackets denoting so.

Mind you, if we want to be extra pedantic - it is not required for
--help, --version et al. Although that should be obvious, as we are
(starting to) simplify yet enhance the documentation.

Signed-off-by: Ricardo Branco <rbranco@suse.de>
[Emil: drop kmod hunk, squash + commit message]
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Lucas De Marchi <demarchi@kernel.org>
Link: https://github.com/kmod-project/kmod/pull/pull/400
Signed-off-by: Lucas De Marchi <demarchi@kernel.org>