x86, vdso: Remove vestiges of VDSO_PRELINK and some outdated comments

These definitions had no effect.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Link: http://lkml.kernel.org/r/946c104e40c47319f8ab406e54118799cb55bd99.1399317206.git.luto@amacapital.net


Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>