[CQ] cleanup some unnecessary ignores

(Discovered while working on: #35234)

Change-Id: Iafd87176cf1e5df0cfa72e5f204ff8514243fbca
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/404340
Reviewed-by: Paul Berry <[email protected]>
Auto-Submit: Phil Quitslund <[email protected]>
Reviewed-by: Johnni Winther <[email protected]>
Commit-Queue: Johnni Winther <[email protected]>

Author: pq

pkg/front_end/lib/src/kernel/body_builder.dart

@@ -9813,7 +9813,6 @@ class BodyBuilder extends StackListenerImpl
     ]));
     reportIfNotEnabled(
         libraryFeatures.patterns, question.charOffset, question.charCount);
-    // ignore: unused_local_variable
     Pattern operand = toPattern(pop());
     push(forest.createNullCheckPattern(question.charOffset, operand));
   }

pkg/front_end/lib/src/source/source_constructor_builder.dart

@@ -509,7 +509,6 @@ class DeclaredSourceConstructorBuilder
       _constructorTearOff ??
       // The case is need to ensure that the upper bound is [Member] and not
       // [GenericFunction].
-      // ignore: unnecessary_cast
       _constructor as Member;
 
   @override

pkg/front_end/lib/src/type_inference/inference_visitor.dart

@@ -9959,7 +9959,6 @@ class InferenceVisitorImpl extends InferenceVisitorBase
     }
 
     List<DartType> positionalTypes;
-    // ignore: UNUSED_LOCAL_VARIABLE
     List<NamedType> namedTypes;
 
     if (namedElements == null) {