Remove unused file transforms

Summary:
Ref T7707.

• Modernize the file transform endpoint a bit.
• Delete transforms which are no longer used in the product.

Test Plan:

• Used Pholio (navigation, inline thumbs).
• Uploaded images (embed thumb).
• Changed profile picture (profile thumb).

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7707

Differential Revision: https://secure.phabricator.com/D12807