Revert "Implemented Request #11100 (session_gc() function)."

This reverts commit 54a42f0d0cf85fe0c032009b1f601427ae1c8566.

Conflicts:
	ext/session/tests/session_gc_basic.phpt
Revert "Implement Bug #54649 Create session_serializer_name()"

This reverts commit 678ec306557f61bf54b6df454387e7d9c3f50de5.

Conflicts:
	ext/session/tests/session_serializer_name_basic.phpt