Remove flavor text for action buttons

Summary: A small but appreciable number of users find flavor on buttons confusing. Remove this flavor. This retains flavor in headers, error messages, etc., which doesn't cause confusion.

Test Plan: Looked at a revision, task, paste, macro, etc.

Reviewers: chad, btrahan

Reviewed By: btrahan

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D8812