GFS2: Remove lockstruct subdir from gfs2 sysfs files

The lockstruct sub directory contained two entries, both of
which are duplicated elsewhere in the gfs2 sysfs files as
well as being available via /proc/mounts. There is no userland program
using either of them, so this patch removes them.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>