libdm: remove dm dev without error even with malformed UUID

libdm: remove dm dev without error even with malformed UUID

On each ioctl return, the device UUID is decoded from \xNN format.
If the UUID of the device being *removed* is malformed (e.g. it
hasn't been corrected before), just remove it without any error
as the UUID is not needed anymore - the device is gone anyway.

Otherwise a misleading error message would be issued just after
the removal:
  # dmsetup remove test
  The UUID "a b" should be mangled but it contains blacklisted characters.
  Command failed