[K2 JS] Unmute and link to issue some JS K2 tests

compiler/testData/codegen/box/when/enumOptimization/kt15806.kt

@@ -1,9 +1,6 @@
-// IGNORE_BACKEND_K2: JS_IR, JS_IR_ES6
 // JVM_ABI_K1_K2_DIFF: KT-62903
 // CHECK_CASES_COUNT: function=doTheThing count=2 TARGET_BACKENDS=JS
-// CHECK_CASES_COUNT: function=doTheThing count=0 IGNORED_BACKENDS=JS
 // CHECK_IF_COUNT: function=doTheThing count=2 TARGET_BACKENDS=JS
-// CHECK_IF_COUNT: function=doTheThing count=4 IGNORED_BACKENDS=JS
 
 private fun Any?.doTheThing(): String {
     when (this) {
@@ -28,4 +25,4 @@ enum class Level {
 
 fun box(): String {
     return "O".doTheThing() + Level.K.doTheThing()
-}
+}