uma: Remove a bogus setbounds operation

It's up to the backend allocator to apply bounds.  When UMA is allocating
memory, this is already done in the keg (slab allocator) layer.  For cache
zones, where UMA is just providing a frontend to some custom allocator, we
shouldn't be touching bounds at all; we don't even know that what we're
allocating is memory, UMA is just providing per-CPU caching for pointer-sized
objects.

sys/vm/uma_core.c

@@ -4483,10 +4483,6 @@ zone_alloc_item(uma_zone_t zone, void *udata, int domain, int flags)
 
 	if (zone->uz_import(zone->uz_arg, &item, 1, domain, flags) != 1)
 		goto fail_cnt;
-#ifdef __CHERI_PURE_CAPABILITY__
-	if ((zone->uz_flags & UMA_ZONE_PCPU) == 0)
-		item = cheri_setboundsexact(item, zone->uz_size);
-#endif
 
 	/*
 	 * We have to call both the zone's init (not the keg's init)