Fix soundness hole in `Table::delete` + don't make & immedately drop PVs in the method

[Centril]

Description of Changes

• There was a soundness hole in Table::delete where we didn't confirm that the row was present.
• In many cases of Table::delete, we make a PV just to immediately drop it. Fixes #1083.

Future work: consider changing Table::find_same_row to work on &ProductValue instead, so we don't have to insert rows temporarily anywhere.

API and ABI breaking changes

None

Expected complexity level and risk

2