e_policy_stack: remove restack children code in e_policy_stack_below/above

e_policy_stack: remove restack children code in e_policy_stack_below/above

There was a bug that the transient_below children was placed above on the parent window
when the parent restacked using stack_above or stack_below.
This was because there was no check code the children's transient_policy.

To fix this problem, we just remove code which restack children in e_policy_stack_below/above
because if the window's stack is changed, then its children will be restacked in
_e_client_cb_evas_restack().

Change-Id: Ib7f832f2d44c3d22b3b924b489206210f9e2cd99