StaticDiff is unused and needs to be shot

StaticDiff is unused, and the last row was added to the table in January 2010. The table is only 30k rows, and roughly 20k of those are not linked to BranchMergeProposal.

We can migrate the linked rows from StaticDiff to PreviewDiffs by the following SQL:

CREATE INDEX temp_previewdiff ON previewdiff(source_revision_id, target_revision_id); (Index creation may not be needed)

INSERT INTO previewdiff (source_revision_id, target_revision_id, diff) SELECT from_revision_id, to_revision_id, diff FROM staticdiff WHERE id IN (SELECT review_diff FROM branchmergeproposal WHERE review_diff IS NOT NULL AND merge_diff IS NULL); (expecting 5,213 rows)

UPDATE branchmergeproposal SET merge_diff = (SELECT id FROM previewdiff WHERE from_revision_id = source_revision_id AND to_revision_id = target_revision_id) FROM staticdiff WHERE staticdiff.id = review_diff AND merge_diff IS NULL; (expecting 5,251 rows)

UPDATE branchmergeproposal SET review_diff = null WHERE review_diff IS NOT NULL AND merge_diff IS NOT NULL; (expecting 12,111 rows)

ALTER TABLE branchmergeproposal DROP CONSTRAINT branchmergeproposal_review_diff_fkey; (drop the FK)