gfs2: remove unused LBIT macros

Since commit 223b2b88 ("GFS2: Fix alignment issue and tidy
gfs2_bitfit"), these 3 macros aren't used anymore, so remove them.

Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>