x86: Remove unused bits from lib/thunk_*.S

Some of the items removed were apparently never used, others
simply didn't get removed with their last user.

Signed-off-by: Jan Beulich <jbeulich@novell.com>
LKML-Reference: <4D6BD3A002000078000341F1@vpn.id2.novell.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>