Remove the repeted word in the PannerNode equalpower Panning (#2577)

index.bs

@@ -13365,7 +13365,7 @@ connections to the input are mono. Otherwise
 PannerNode "equalpower" Panning</h4>
 
 This is a simple and relatively inexpensive algorithm which
-provides basic, but reasonable results. It is used for the for the
+provides basic, but reasonable results. It is used for the
 {{PannerNode}} when the {{PannerNode/panningModel}} attribute is set to
 "{{PanningModelType/equalpower}}", in which case the <em>elevation</em>
 value is ignored. This algorithm MUST be implemented using