KVM: remove pre_task_link setting in save_state_to_tss16

Now, also remove pre_task_link setting in save_state_to_tss16.

  commit b237ac37
  Author: Gleb Natapov <gleb@redhat.com>
  Date:   Mon Mar 30 16:03:24 2009 +0300

    KVM: Fix task switch back link handling.

CC: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>