remove support for 'trait' keyword

js/js.translator/testData/classObject/cases/inTrait.kt

@@ -1,6 +1,6 @@
 package foo
 
-trait A {
+interface A {
     companion object {
         val OK: String = "OK"
     }

js/js.translator/testData/classObject/cases/namedClassObject.kt

@@ -1,6 +1,6 @@
 package foo
 
-trait Named {
+interface Named {
     companion object Bar {
         val g = "a";
     }