FIR: unmute passing black-box tests (nested constructor resolve)

compiler/testData/codegen/box/privateConstructors/base.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 // See also KT-6299
 public open class Outer private constructor() {
     class Inner: Outer()

compiler/testData/codegen/box/privateConstructors/withArguments.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 // See also KT-6299
 public open class Outer private constructor(val s: String, val f: Boolean = true) {
     class Inner: Outer("xyz")

compiler/testData/codegen/box/privateConstructors/withDefault.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 // See also KT-6299
 public open class Outer private constructor(val x: Int = 0) {
     class Inner: Outer()

compiler/testData/codegen/box/privateConstructors/withLinkedClasses.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 // See also KT-6299
 public open class Outer private constructor(val p: Outer?) {
     object First: Outer(null)

compiler/testData/codegen/box/regressions/kt18779.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 sealed class Result {
     class Failure(val exception: Exception) : Result()
     class Success(val message: String) : Result()