KVM: Simplify kvm_timer

'reinject' is never initialized
't_ops' only serves as indirection to lapic_is_periodic; call that directly
   instead
'kvm' is never used
'vcpu' can be derived via container_of

Remove these fields.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>