xfs: fix online repair block reaping

These patches fix a few problems that I noticed in the code that deals
with old btree blocks after a successful repair. First, we clarify how
the reaping function works w.r.t. bitmap lifetimes.  Next we fix a bug
where we could incorrectly invalidate old btree blocks if they were
crosslinked.  Finally, we convert the reap function to use EFIs so that
we can delete blocks without overloading a transaction.
-----BEGIN PGP SIGNATURE-----
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=HlU4
-----END PGP SIGNATURE-----