Revert "validate that the host entity for a registration permits new...

Revert "validate that the host entity for a registration permits new registrations and whether the user being registered has permission to register at the controller level before saving a registration. previously we were only checking at the form level so users could create multiple registerations for a single user even if multiple registrations were not permitted by creating two inactive registrations and then moving each into an active state. also a user could register for an event that had reached capacity since the inactive registration was created"

This reverts commit 3960760b.