x86: remove additional vestiges of the zImage/bzImage split

Impact: cleanup

Remove targets that were used for zImage only, and Makefile
infrastructure that was there to support the zImage/bzImage split.

Reported-by: Paul Bolle <pebolle@tiscali.nl>
LKML-Reference: <1236879901.24144.26.camel@test.thuisdomein>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>