USELESS_ELVIS_RIGHT_IS_NULL : build fix (add to different files in DiagnosticsTestGenerated), do not report if USELESS_ELVIS already exists

(cherry picked from commit c71b656)

compiler/testData/diagnostics/tests/smartCasts/elvisExprNotNull.kt

@@ -30,7 +30,7 @@ fun baz(s: String?, r: String?): String {
 }
 
 fun withNull(s: String?): String {
-    val t = s ?: null
+    val t = s <!USELESS_ELVIS_RIGHT_IS_NULL!>?: null<!>
     // Error: nullable
     return <!TYPE_MISMATCH!>t<!>
 }