[GFS2] Remove gfs2_check_acl()

As pointed out by Adrian Bunk, the gfs2_check_acl() function is no
longer used. This patch removes it and renamed gfs2_check_acl_locked()
to gfs2_check_acl() since we only need one variant of that function now.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Cc: Adrian Bunk <bunk@stusta.de>