R1:d4b6b095cbf7

Provide a script to completely destroy revisions

Summary:
Someone may or may not have accidentally uploaded secrets to Differential. Provide an administrative mechanism to permanently destroy a revision.

Also fix some of the transaction handling code.

Test Plan:
$ ./scripts/differential/destroy_revision.php --trace D1
>>> [0] <connect>
<<< [0] <connect> 1,060 us
>>> [1] <query> SELECT * FROM `differential_revision` WHERE `id` = 1
<<< [1] <query> 473 us

Really destroy 'D1: asdbas'…