[FE 1.0] Correctly set USED_AS_EXPRESSION for unreachable when and if blocks

^KT-50028 Fixed

compiler/testData/codegen/box/controlStructures/returnsNothing/ifElse.kt

@@ -1,6 +1,3 @@
-// IGNORE_BACKEND: WASM
-// WASM_MUTE_REASON: STRANGE_IMPLICIT_CAST
-
 fun kt49182(x: Boolean): String {
     return if (x) {
         return "O"
@@ -23,4 +20,4 @@ fun box(): String {
         exit()
     }
     return a
-}
+}