KVM: x86 emulator: Use em_push() instead of emulate_push()

em_push() is a simple wrapper of emulate_push().  So this patch replaces
emulate_push() with em_push() and removes the unnecessary former.

In addition, the unused ops arguments are removed from emulate_pusha()
and emulate_grp45().

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: Avi Kivity <avi@redhat.com>