Remove "Apply Patch" UI field from Differential

Summary: Ref T12026. This simplifies the UI and makes T11114 easier. I plan to integrate this into "Download Raw Diff" in the future.

Test Plan:

• Browsed revisions.
• Grepped for removed class name.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12026

Differential Revision: https://secure.phabricator.com/D17069