[tests] don't use js.Promise

tests/unit/src/unit/issues/Issue7890.hx

@@ -2,16 +2,7 @@ package unit.issues;
 
 class Issue7890 extends unit.Test {
 	function test() {
-		#if js
-		var p = js.Promise.resolve('hi');
-
-		p.then(
-			(string) -> {
-				return;
-			}, (error) -> {
-				trace(error);
-			});
-		#end
+		var x: () -> Void = () -> { return; }
 		noAssert();
 	}
 }