docs(readme): remove obsolete code from usage example
docs(readme): remove obsolete code from usage example

bajzarpa/angular-facebook,Ciul/angular-facebook,karthiksekarnz/angular-facebook,ofirgott/angular-facebook,bajzarpa/angular-facebook,ofirgott/angular-facebook,karthiksekarnz/angular-facebook,Ciul/angular-facebook,BenjaminCh/angular-facebook,BenjaminCh/angular-facebook