[Test] Disable UNUSED_* diagnostics in tests which are not belong to contolFlowAnalysis suite

compiler/testData/diagnostics/tests/Casts.kt

@@ -15,7 +15,7 @@ fun test() : Unit {
   checkSubtype<Int?>(x as? Int?)
   checkSubtype<Int?>(y as? Int?)
 
-  val <!UNUSED_VARIABLE!>s<!> = "" as Any
+  val s = "" as Any
   ("" as String?)?.length
   (<!REDUNDANT_LABEL_WARNING!>data@<!>("" as String?))?.length
   (<!WRONG_ANNOTATION_TARGET!>@MustBeDocumented()<!>( "" as String?))?.length