op.c:opslab_force_free: Make paranoid code reflect reality

op.c:opslab_force_free: Make paranoid code reflect reality

When opslab_force_free is called, the CV still has a reference count
on the slab.  In fact, we don’t even bother lowering it if all goes
well, but simply free the slab with the reference count set to 1.
So the paranoid code that increments the reference count before free-
ing an op is not necessary.  Also, the shortcut out of the loop
was never triggered, as it was checking for a reference count of 0,
rather than 1.