KVM: VMX: remove yield_on_hlt

yield_on_hlt was introduced for CPU bandwidth capping. Now it is
redundant with CFS hardlimit.

yield_on_hlt also complicates the scenario in paravirtual environment,
that needs to trap halt. for e.g. paravirtualized ticket spinlocks.

Acked-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>