Removed add-ons from the repository

Dropped usage of github submodule feature to provide the add-ons.

Author: intjelic

.gitmodules

@@ -14,18 +14,6 @@ the following command to obtain the source::
     git clone git@github.com:Sonkun/python-sfml.git
     cd python-sfml
 
-The source from the add-ons projects are available as submodules, which may be
-obtained by issuing the following additional commands::
-
-    git submodule init
-    git submodule update
-
-Alternatively, you may clone the main project and its submodules all at once
-with the following command::
-
-    git clone --recursive git://github.com/Sonkun/python-sfml.git
-    cd python-sfml
-
 Resources
 =========
 * Website: http://python-sfml.org