Delete QAOA docs moved to ReCirq, remove links (#5452)

Three QAOA tutorials were moved to ReCirq in PR quantumlib/ReCirq#293. 
This PR deletes the three of them as well as redirecting the only remaining link to them (in `tutorials/_index.yaml`). 

Should only be merged with cl/453216799

Author: augustehirth

docs/tutorials/_index.yaml

@@ -25,7 +25,7 @@ landing_page:
           name: menu_book
       - heading: Approximate optimization
         description: Use a quantum computer to find approximately optimal cuts in a graph.
-        path: /cirq/tutorials/qaoa
+        path: /cirq/experiments/qaoa_maxcut
         icon:
           name: menu_book
       - heading: Quantum walks