Port registry.el the rest of the way to cl-lib

Port registry.el the rest of the way to cl-lib

This file already is using cl-lib functions at runtime; eieio ultimately
loads cl-lib, which explains why doing so wasn't an issue.
* lisp/registry.el: Require cl-lib.
(registry-db, registry--match, registry-search, registry-delete):
(registry-insert, registry-reindex): Replace cl macros with cl-lib ones.
(registry-collect-prune-candidates): Replace cl function with cl-lib one.