While `do_versions_after_setup` does more than what was previously done
by link/append code (essentially also handles pre-2.50 IPO and sound
proxy conversions), there is no real fundamental reasons to not use it
in linking code.
The IPO and sound proxy conversion codes are likely fully broken for
linked data - but they should then be removed or fixed, since they will
be applied on linked data in blendfile reading case anyway.
And in general, versioning should 'just work' the same when loading a
whole blendfile, or linking some data from a library. Keeping things
separate only makes it harder to work with, and easier to hide issues
with linked data.
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