Add assertion in expand_vacuum_rel() for non-autovacuum path
The code path where the assertion is added helps to check that
autovacuum always includes a relation OID when doing a vacuum on it.
Extracted from a larger patch set to add support for SKIP LOCKED with
manual VACUUM commands.
Author: Nathan Bossart
Discussion: https://postgr.es/m/
9EF7EBE4-720D-4CF1-9D0E-
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