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