removed gitdb submodule

Author: Byron

.gitmodules

@@ -1,7 +1,3 @@
-[submodule "gitdb"]
-	path = git/ext/gitdb
-	url = git://github.com/gitpython-developers/gitdb.git
-	branch = master
 [submodule "git/ext/async"]
 	path = git/ext/async
 	url = git://github.com/gitpython-developers/async.git