tick: Assume timekeeping is correctly handed over upon last offline idle call

The timekeeping duty is handed over from the outgoing CPU on stop
machine, then the oneshot tick is stopped right after.  Therefore it's
guaranteed that the current CPU isn't the timekeeper upon its last call
to idle.

Besides, calling tick_nohz_idle_stop_tick() while the dying CPU goes
into idle suggests that the tick is going to be stopped while it is
actually stopped already from the appropriate CPU hotplug state.

Remove the confusing call and the obsolete case handling and convert it
to a sanity check that verifies the above assumption.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240225225508.11587-16-frederic@kernel.org