Remove lockingfailed().

Remove lockingfailed().

  We provide a lock type that behaves like no_locking, but is not
  clustered. Moreover, it also forbids any write locks. This magically (and
  consistently) prevents use of clustered VGs, or changing local VGs with
  --ignorelockingfailure. As a bonus, we can remove the special hacks in a few
  places. Of course, people looking for trouble can always set their locking_type
  to 0 to override.