Destroy surplus columns

Summary:
Ref T1191. This destroys surplus columns:

  - Pholio's transaction comments have a `mockID` column, but this is not used. The `imageID` column is used instead.
  - Phragment has an unused `description` column.
  - Releeph has an unused `summary` column.

Test Plan:
  - Grepped for usage of these columns.
  - Checked that these exist in production, too.
  - Ran upgrades.
  - Added Pholio inline comments.
  - Saw fewer warnings.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley, hach-que

Maniphest Tasks: T1191

Differential Revision: https://secure.phabricator.com/D10591