Refactor: based: Move cib_msg_copy() to based_messages.c

And make it static. It's logically message-related, and the only caller
is sync_our_cib().

Also remove the CRM_CHECK() for replace_request non-NULL. cib_msg_copy()
asserts if it's NULL.

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>