[connections] Commented out Ssh.upload

This method is not used yet but it will be in the future.
For the moment we can avoid adding tests for it and keep it commented out.

openwisp_controller/connection/connectors/ssh.py

@@ -122,11 +122,13 @@ def exec_command(self, command, timeout=SSH_COMMAND_TIMEOUT,
     def update_config(self):
         raise NotImplementedError()
 
-    def upload(self, fl, remote_path):
-        scp = SCPClient(self.shell.get_transport())
-        if not hasattr(fl, 'getvalue'):
-            fl_memory = BytesIO(fl.read())
-            fl.seek(0)
-            fl = fl_memory
-        scp.putfo(fl, remote_path)
-        scp.close()
+    # TODO: this method is not used yet
+    # but will be necessary in the future to support other OSes
+    # def upload(self, fl, remote_path):
+    #     scp = SCPClient(self.shell.get_transport())
+    #     if not hasattr(fl, 'getvalue'):
+    #         fl_memory = BytesIO(fl.read())
+    #         fl.seek(0)
+    #         fl = fl_memory
+    #     scp.putfo(fl, remote_path)
+    #     scp.close()