Remove "searchproject" typeahead datasource

Summary: Ref T4420. This is just "project", plus the special "no project" token, but that doesn't actually work. Replace it with a normal project typeahead. This is only used in Maniphest's reports.

Test Plan: Searched for a couple of projects in reports.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T4420

Differential Revision: https://secure.phabricator.com/D9890