Merge pull request #5002 from gero3/FixMemoryProblem

fix the way of removeing a mesh

src/renderers/WebGLRenderer.js

@@ -4021,7 +4021,7 @@ THREE.WebGLRenderer = function ( parameters ) {
 
 	function removeInstancesWebglObjects( objlist, object ) {
 
-		delete objlist[object]; 
+		delete objlist[object.id]; 
 
 	};