cpuidle: haltpoll: Remove single state handling

cpuidle: haltpoll: Remove single state handling

cpuidle systems where the governor has no choice because there's only
a single idle state are now handled by cpuidle core and bypass the
governor, so remove the related handling.

Signed-off-by: Aboorva Devarajan <aboorvad@linux.ibm.com>
Reviewed-by: Christian Loehle <christian.loehle@arm.com>
[ rjw: Extended the change to drop a redundant local variable ]
Link: https://patch.msgid.link/20260216185005.1131593-3-aboorvad@linux.ibm.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>