Migrate to built-in Go vendoring.

This also removes `godep` calls from make scripts. Of note is that
currently `./...` checking in acceptance tests is disabled.

vendor/github.com/google/go-github/github/git.go

@@ -0,0 +1,14 @@
+// Copyright 2013 The go-github AUTHORS. All rights reserved.
+//
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package github
+
+// GitService handles communication with the git data related
+// methods of the GitHub API.
+//
+// GitHub API docs: http://developer.github.com/v3/git/
+type GitService struct {
+	client *Client
+}