pgsql: Put back intra-grant-inplace.spec test coverage

Put back intra-grant-inplace.spec test coverage

Commit d31bbfb6590 lost some test coverage, because the situation
being tested, a concurrent DROP, cannot happen anymore.  Put the test
coverage back with a bit of a trick, by deleting directly from the
catalog table.

Co-authored-by: Noah Misch <noah@leadboat.com>
Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
Discussion: https://www.postgresql.org/message-id/flat/bf72b82c-124d-4efa-a484-bb928e9494e4@eisentraut.org

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/310d04169a41c20fa2e84ba6e40cffc10b8fa065

Modified Files
--------------
src/test/isolation/expected/intra-grant-inplace.out | 4 ++--
src/test/isolation/specs/intra-grant-inplace.spec   | 2 +-
2 files changed, 3 insertions(+), 3 deletions(-)