Remove PhabricatorPHIDAllocateController

Summary:
This is not very useful and not exposed on the web UI. It's also the only caller
for PhabricatorPHIDConstants::getTypes().

I originally wrote this to test PHID allocation when I built the PHID system but
it's no longer really useful in any way.

phid.allocate might be useful to expose over Conduit eventually but the
implementation is trivial.

Test Plan: Grepped for controller and method names, came up empty.
Reviewed By: codeblock
Reviewers: jungejason, tuomaspelkonen, aran, codeblock
CC: aran, codeblock
Differential Revision: 625