xfstests: remove bench infrastructure

xfstests: remove bench infrastructure

The benchmark framework inside xfstests is basically unused,
bitrotted and not very useful. If we need benchmarks, lets use a
real benchmark framework, not xfstests. Kill it to remove
dependencies on common and common.rc.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Phil White <pwhite@sgi.com>
Signed-off-by: Rich Johnston <rjohnston@sgi.com>