Remove rows for personal saved builtin queries

Summary:
Ref T12956. After this change, individual users will no longer be able to modify builtin queries on a user-by-user basis: they will always appear at the bottom of the list, under their personal queries, and can only be managed by administrators.

To support this, clean up the old rows which could be hanging around from before: delete any personal saved queries where the saved query is a builtin query.

To ease this transition, try to pin the query we're deleting if the user had reordered things to put it on top.

Test Plan:

• Ran the migration, saw no changes in the UI but fewer rows.
• Went back to master, reordered queries to put a builtin one on top.
• Ran the migration.
• Saw that builtin one drop to the bottom (since it can't be on top anymore) but be pinned, preserving the behavior of /maniphest/.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12956

Differential Revision: https://secure.phabricator.com/D18464