R1:2845d1196202

Remove PhabricatorPHID::fromObjectName

Summary: Ref T2715. This only ever supported like 10% of object types; get rid of it in favor of the new infra.

Test Plan:
- Ran `bin/search index D12`; `bin/search index <some valid phid>`, `bin/search index derp`.
- Turned off Search jump, searched for `D12`.
- Used `phid.lookup`.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2715

Differential Revision: https://secure.phabricator.com/D6519