src: consistently use _(Str) instead of gettext(Str)

src: consistently use _(Str) instead of gettext(Str)

Make use of the _(Str) macro provided by <config.h>.

The change was made automatically using the following command:
$ git grep -l '\<gettext *(' src |xargs sed -i 's/\<gettext *(/_(/g'

(cherry-picked from commit 3ddd8f9bb62b20c62a74d7ded5c7f36783f9b761)

Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
Signed-off-by: Dongkyun Son <dongkyun.s@samsung.com>