[FIR] fix false negative MUST_BE_INITIALIZED for deferred init + custom setter case

^KT-58346 Fixed
Review: https://jetbrains.team/p/kt/reviews/9967

BTW this commit accidentaly and partially fixes KT-57553 for K2, because
of a cleaner K2 architecture. I will unify MUST_BE_INITIALIZED behaviour
in K1 and K2 in the next commits

compiler/testData/ir/irText/classes/initVar.kt.txt

@@ -59,37 +59,3 @@ class TestInitVarWithCustomSetter {
 
 }
 
-class TestInitVarWithCustomSetterWithExplicitCtor {
-  var x: Int
-    get
-    set(value: Int) {
-      <this>.#x = value
-    }
-
-  init {
-    <this>.<set-x>(value = 0)
-  }
-
-  constructor() {
-    super/*Any*/()
-    /* <init>() */
-
-  }
-
-}
-
-class TestInitVarWithCustomSetterInCtor {
-  var x: Int
-    get
-    set(value: Int) {
-      <this>.#x = value
-    }
-
-  constructor() {
-    super/*Any*/()
-    /* <init>() */
-
-    <this>.<set-x>(value = 42)
-  }
-
-}