Rewrite PrimaryEntityRelationDelete to be a concrete check for issues without a project

The checks is written in a very abstract manner but we only use it to search for orphan issues (issues without a project). We should:

1. rewrite and rename the check to be more specific so it is not confusing
2. rewrite the check to use a database join rather than loop through all the issues to speed things up
3. delete the issue through the manager to ensure all issue's dependencies are removed
4. javadoc the class