doc: announce removal of lcore state finished

doc: announce removal of lcore state finished

Lcore state FINISHED is used by the worker thread to indicate that
it has completed the assigned task. The state is changed to
WAIT by another thread after it observes the updated state. This
additional step is redundant. After this deprecation, the worker
thread will update the state to WAIT.

Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
Acked-by: Feifei Wang <feifei.wang2@arm.com>
Acked-by: Jerin Jacob <jerinj@marvell.com>
Acked-by: Thomas Monjalon <thomas@monjalon.net>