Revert "'yield' reserved as a keyword"

This reverts commit 434082cadb.

js/js.translator/testData/reservedWords/cases/insideClassObjectVarClass.kt

@@ -0,0 +1,19 @@
+package foo
+
+// NOTE THIS FILE IS AUTO-GENERATED by the generateTestDataForReservedWords.kt. DO NOT EDIT!
+
+class TestClass {
+    companion object {
+        var `class`: Int = 0
+
+        fun test() {
+            testNotRenamed("class", { `class` })
+        }
+    }
+}
+
+fun box(): String {
+    TestClass.test()
+
+    return "OK"
+}