Remove localhost Drydock allocator

Summary: This has never been enabled by default, and isn't safe.  Remove it since people can use preallocated or EC2 hosts.

Test Plan: Removed it; didn't see it appear on the "Create Blueprint" page.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D10287