Merge pull request #21311 from mrdoob/Mugen87-patch-1

Matrix3: Remove superfluous  copy.

src/math/Matrix3.js

@@ -198,7 +198,7 @@ class Matrix3 {
 
 	getNormalMatrix( matrix4 ) {
 
-		return this.setFromMatrix4( matrix4 ).copy( this ).invert().transpose();
+		return this.setFromMatrix4( matrix4 ).invert().transpose();
 
 	}