util: make mesa-sha1.c completely empty when there are no SHA1 impls

util: make mesa-sha1.c completely empty when there are no SHA1 impls

My earlier attempt to fix this missed the fact that there was a #else
clause that assumes that you have openssh. This moves the whole thing
under #ifdef HAVE_SHA1 which should avoid this issue.

Fixes: 13bfa5201 (util: always include sha1 into the build)
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91898
Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Dave Airlie <airlied@gmail.com>