InstancedBufferGeometry: Removed redundant clone() code.

src/core/InstancedBufferGeometry.js

@@ -23,12 +23,6 @@ class InstancedBufferGeometry extends BufferGeometry {
 
 	}
 
-	clone() {
-
-		return new this.constructor().copy( this );
-
-	}
-
 	toJSON() {
 
 		const data = super.toJSON();