Revert "rra/zhelenskiy/flattening_impl"

This reverts commit b7f5c039a6.

compiler/testData/codegen/box/valueClasses/forStatement.kt

@@ -1,16 +0,0 @@
-// WITH_STDLIB
-// TARGET_BACKEND: JVM_IR
-// WORKS_WHEN_VALUE_CLASS
-// LANGUAGE: +ValueClasses
-
-@JvmInline
-value class DPoint(val x: Double, val y: Double)
-
-fun box(): String {
-    var res = 0.0
-    for (x in listOf(DPoint(1.0, 2.0), DPoint(3.0, 4.0))) {
-        res += x.x + x.y
-    }
-    require(res == 10.0)
-    return "OK"
-}