s390: remove compat vdso code

Remove compat vdso code, since there is hardly any compat user space
left. Still existing compat user space will have to use system calls
instead.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>