Remove glusterfs_disk_util option

The glusterfs_disk_util option has been removed. I have manually
removed this entry from the current configuration tables and the
flag mapping.

As it is no longer in the code it will also no longer appear in
future auto-generated versions of the tables.

Closes-Bug: #1259419

Change-Id: I4aa606b3920347caa896c5b65ddcff6d9faf9881
Merge "Remove glusterfs_disk_util option"