Code used to tag liboverrides references as 'pre-existing' to force code
further down the way to always keep these IDs linked.
However, this was a (bad) hack, since it could have uncontrollable
side-effects, abusing a tag for somethig else than its original meaning.
And this should not have been needed for quite some time already, as
liboverrides handling was already properly done by append
post-processing code.
No behavior change expected here.
4d944c5491