fix(ext): stop importing git-submodules for gitdb & smmap

Stop importing on runtime submodules of this project: gitdb, smmap.  
This overrides any other 
method of setting `SYSPATH`, eg:
- pip install -e ./gitdb.git
- pip install -e .
- pip install git+https://...
- dependent projects for IDes(LiClipse & PyCharm).
- Manual maintain path.

Author: ankostis

Diff for: git/__init__.py

@@ -15,24 +15,6 @@
 __version__ = 'git'
 
 
-#{ Initialization
-def _init_externals():
-    """Initialize external projects by putting them into the path"""
-    if __version__ == 'git':
-        sys.path.insert(0, osp.join(osp.dirname(__file__), 'ext', 'gitdb'))
-
-    try:
-        import gitdb
-    except ImportError:
-        raise ImportError("'gitdb' could not be found in your PYTHONPATH")
-    # END verify import
-
-#} END initialization
-
-#################
-_init_externals()
-#################
-
 #{ Imports
 
 from git.config import GitConfigParser  # @NoMove @IgnorePep8