Remove "File Name" search tool

Summary: Removing this cleanly in event we want to put it back later. 99% of these cases are likely workable either by command line or the typeahead. Will gauge feedback if users notice.

Test Plan: Reload page, perform file grep search.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D18425