Remove the (rather pointless) callback server CLI

The callback server CLI only printed received text message which can
also be done easily with the callback server example.

Author: lgrahl

README.rst

@@ -97,19 +97,6 @@ command:
 
     $ threema-gateway version
 
-Callback Server
----------------
-
-The callback server can be used to receive messages. The demo script
-``threema-callback-server`` prints out received message on the command
-line. Run the following command to see usage information.
-
-.. code-block:: bash
-
-    $ threema-callback-server --help
-
-The script resides `here <threema/gateway/bin/callback_server.py>`_.
-
 Troubleshooting
 ***************
 

setup.py

@@ -77,7 +77,6 @@ def read(file):
     entry_points={
         'console_scripts': [
             'threema-gateway = threema.gateway.bin.gateway_client:main',
-            'threema-callback-server = threema.gateway.bin.callback_server:main',
         ],
     },