Compeltely remove the replaces functionality and move all overrides
handling to getVar time. We can move the cookie cache into a hidden
flag within the variables themselves.
This removes the need for any of the internal_finalize steps.
This obsolete the need for the _seen_overrides COW cache.
(Bitbake rev: 2a0b73110bede91777ada54d1d89b45fb6034b6c)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>