JS: refactor generation of callable references to functions

compiler/testData/codegen/box/callableReference/bound/kCallableNameIntrinsic.kt

@@ -1,5 +1,3 @@
-// Enable when callable references to builtin members is supported
-// IGNORE_BACKEND: JS
 fun box(): String {
     var state = 0
     val name = (state++)::toString.name

compiler/testData/codegen/box/callableReference/bound/kt12738.kt

@@ -1,5 +1,3 @@
-// Enable when callable references to builtin members is supported
-// IGNORE_BACKEND: JS
 fun <T> get(t: T): () -> String {
     return t::toString
 }

compiler/testData/codegen/box/callableReference/bound/kt15446.kt

@@ -1,5 +1,4 @@
 //WITH_RUNTIME
-// IGNORE_BACKEND: JS
 fun box(): String {
     val a = intArrayOf(1, 2)
     val b = arrayOf("OK")

compiler/testData/codegen/box/callableReference/bound/simpleFunction.kt

@@ -1,5 +1,3 @@
-// Enable when callable references to builtin members is supported
-// IGNORE_BACKEND: JS
 fun box(): String {
     val f = "KOTLIN"::get
     return "${f(1)}${f(0)}"