Remove Matrix3.multiplyToArray

This is due to the removal of the Matrix4 equivalent in d8f7ccf2

src/math/Matrix3.js

@@ -156,20 +156,6 @@ Object.assign( Matrix3.prototype, {
 
 	},
 
-	multiplyToArray: function ( a, b, r ) {
-
-		var te = this.elements;
-
-		this.multiplyMatrices( a, b );
-
-		r[ 0 ] = te[ 0 ]; r[ 1 ] = te[ 1 ]; r[ 2 ] = te[ 2 ];
-		r[ 3 ] = te[ 3 ]; r[ 4 ] = te[ 4 ]; r[ 5 ] = te[ 5 ];
-		r[ 6 ] = te[ 6 ]; r[ 7 ] = te[ 7 ]; r[ 8 ] = te[ 8 ];
-
-		return this;
-
-	},
-
 	multiplyScalar: function ( s ) {
 
 		var te = this.elements;