remove support for 'trait' keyword

js/js.translator/testData/examples/cases/funDelegation.kt

@@ -2,7 +2,7 @@ open class Base() {
     fun n(n: Int): Int = n + 1
 }
 
-trait Abstract {
+interface Abstract {
 }
 
 class Derived1() : Base(), Abstract {

js/js.translator/testData/examples/cases/propertyDelegation.kt

@@ -10,7 +10,7 @@ open class Base() {
         }
 }
 
-trait Abstract {
+interface Abstract {
 }
 
 class Derived1() : Base(), Abstract {

js/js.translator/testData/examples/cases/rightHandOverride.kt

@@ -1,6 +1,6 @@
 // Changed when traits were introduced. May not make sense any more
 
-trait Left {
+interface Left {
 }
 open class Right() {
     open fun f() = 42

js/js.translator/testData/examples/sortedTests/unsupported/basicmethod.kt

@@ -1,6 +1,6 @@
 import java.util.ArrayList
 
-trait Tr {
+interface Tr {
     fun extra(): String = "_"
 }
 

js/js.translator/testData/examples/sortedTests/unsupported/enclosed.kt

@@ -1,8 +1,8 @@
-trait BK {
+interface BK {
     fun x(): Int = 50
 }
 
-trait K : BK {
+interface K : BK {
     override fun x(): Int = super.x() * 2
 }
 

js/js.translator/testData/examples/sortedTests/unsupported/inheritance.kt

@@ -2,7 +2,7 @@
 
 open class X(val x: Int) {
 }
-trait Y {
+interface Y {
     abstract val y: Int
 }
 
@@ -13,7 +13,7 @@ class Point(x: Int, yy: Int) : X(x), Y {
     override val y: Int = yy
 }
 
-trait Abstract {
+interface Abstract {
 }
 
 class P1(x: Int, yy: Y) : Abstract, X(x), Y by yy {

js/js.translator/testData/examples/sortedTests/unsupported/traitproperty.kt

@@ -1,4 +1,4 @@
-trait M {
+interface M {
     var backingB: Int
     var b: Int
         get() = backingB