move Js-specific optimization test to TestJs

tests/optimization/run.hxml

@@ -1,4 +1,5 @@
 -cp src
 -js testopt.js
 --macro Macro.register('Test')
+--macro Macro.register('TestJs')
 -dce std

tests/optimization/src/Test.hx

@@ -78,19 +78,6 @@ class Test {
 		}
 		b.x = a;
 	}
-	@:js("var x = 10;\"\" + x;var x1 = 10;\"\" + x1;var x2 = 10.0;\"\" + x2;var x3 = \"10\";x3;var x4 = true;\"\" + x4;")
-	static function testStdString() {
-        var x = 10;
-        Std.string(x);
-        var x:UInt = 10;
-        Std.string(x);
-        var x = 10.0;
-        Std.string(x);
-        var x = "10";
-        Std.string(x);
-        var x = true;
-        Std.string(x);
-	}
 	
 	@:js('
 		var x_foo = 1;