Drop domain key on PhameBlog
Summary: Right now you can't create two blogs without a domain name, since it has a unique key on the column. Removing the key.
Test Plan: Create two blogs with no domain name, works as expected. Create two blogs with cat.dog as domain name, get duplicate domain error.
Reviewed By: epriestley
Maniphest Tasks: T9360
Differential Revision: https://secure.phabricator.com/D14915