docs(backend): removed section optimization

* already covered

documentation/Application/Backend/optimization.md

-Few words on optimization
-===============
-
-TODO optimization of the request.

documentation/_sidebar.md

@@ -20,7 +20,6 @@
     * [API](Application/Backend/API.md)
     * [External data](Application/Backend/external_data.md)
     * [Tests](Application/Backend/tests.md)
-    * [Optimization](Application/Backend/optimization.md)
 
   - Frontend