Almost one year has passed since all post_as_copy related code
removed by [1], we don't have to keep the warning message for
post_as_copy setting anymore in the code tree.
1: 1e79f828ad10918bd76ae8df6fe4c4dbf7bbf3c5
Change-Id: Id9eea22ed688574d84ca582584c0c207d5f01383