Fixed test for KT-6530 Do not report "useless cast" when RHS is unresolved

compiler/testData/diagnostics/tests/Casts.kt

@@ -13,6 +13,4 @@ fun test() : Unit {
   x <!USELESS_CAST!>as? Int?<!> : Int?
   y <!USELESS_CAST_STATIC_ASSERT_IS_FINE!>as? Int?<!> : Int?
   Unit
-
-  x as <!UNRESOLVED_REFERENCE!>UnresolvedType<!>
 }

compiler/testData/diagnostics/tests/cast/bare/ToErrorType.kt

@@ -1,6 +1,6 @@
 class P
 
 fun foo(p: P): Any {
-    val v = p <!USELESS_CAST_STATIC_ASSERT_IS_FINE!>as <!UNRESOLVED_REFERENCE!>G<!><!>
+    val v = p as <!UNRESOLVED_REFERENCE!>G<!>
     return <!DEBUG_INFO_ELEMENT_WITH_ERROR_TYPE!>v<!>
 }