Drop maniphest_savedquery table

Summary: This data was migrated by D6977 and is now obsolete. I'll hold this patch for a week or two in case we get reports of migration errors.

Test Plan: Ran storage upgrade, saw the table vanish. Grepped for references to the table.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D6997