Remove getPath()

When getting the path and providing an enterprise url for the apiUrl, the /api/v3 portion gets duplicated.  Since they will be combined on line 231 of GitHub.java there is no point just grabbing the path.  See https://github.com/janinko/ghprb/issues/178, and https://issues.jenkins-ci.org/browse/JENKINS-24145?focusedCommentId=208270#comment-208270