res_sorcery_memory_cache: Disallow per-object expire with full backend.

res_sorcery_memory_cache: Disallow per-object expire with full backend.

The AMI action and CLI command did not take into account the properties
of full backend caching. This resulted in an expired object remaining
removed until a full backend update occurred, instead of having the
object updated when needed.

This change makes it so that the AMI action and CLI command for object
expire will now fail instead of putting the cache into an undesired
state. If full backend caching is enabled then only operations
which act on the entire cache are available.

ASTERISK-28942

Change-Id: Id662d888f177ab566c8e802ad583083b742d21f4