[Flang] Fix for CI failure, Remove default case

Remove default case when all the enum values are covered in switch
statements.

Author: kiranchandramohan

flang/lib/Semantics/check-omp-structure.cpp

@@ -981,8 +981,6 @@ void OmpStructureChecker::CheckCancellationNest(
         eligibleCancellation = true;
       }
       break;
-    default:
-      break;
     }
     if (!eligibleCancellation) {
       context_.Say(source,
@@ -1028,8 +1026,6 @@ void OmpStructureChecker::CheckCancellationNest(
           parser::ToUpperCaseLetters(
               parser::OmpCancelType::EnumToString(type)));
       break;
-    default:
-      break;
     }
   }
 }