daemon/blkid.c: Fix compilation error introduced by earlier change

blkid.c: In function ‘test_blkid_p_i_opt’:
  blkid.c:105:3: error: label ‘command_failed’ defined but not used [-Werror=unused-label]
    105 |   command_failed:
        |   ^~~~~~~~~~~~~~

Fixes: https://github.com/libguestfs/libguestfs/pull/315
Fixes: commit ff4467a1a4

daemon/blkid.c

@@ -102,7 +102,6 @@ test_blkid_p_i_opt (void)
   r = commandr (NULL, &err, "blkid", "-p", "/dev/null", NULL);
   if (r == -1) {
     /* This means we couldn't run the blkid command at all. */
-  command_failed:
     reply_with_error ("could not run 'blkid' command: %s", err);
     return -1;
   }