One DO-block ran every DROP in a single transaction and exhausted
max_locks_per_transaction on large schemas (gitlab); emit one DROP per
row and execute via \gexec instead. Also drop user-owned non-public
schemas so a dump that CREATE SCHEMAs (discourse) does not abort on the
existing schema under ON_ERROR_STOP.
Covered by a new DinD e2e test restoring --empty against a fully
populated database with a non-public schema and every object class.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
