Remove some unnecessary ignore comments in test_runner

Change-Id: Ic4dd24a689d6832e4bfe6f1f42abd0c81bcd42e9
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/274731
Reviewed-by: William Hesse <whesse@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>

pkg/test_runner/lib/src/command_output.dart

@@ -1456,7 +1456,6 @@ mixin _StaticErrorOutput on CommandOutput {
   /// Same as `int.parse`, but allows nulls to simply pass through.
   static int? _parseNullableInt(String? s) {
     if (s == null) {
-      // ignore: avoid_returning_null
       return null;
     }
     return int.parse(s);

pkg/test_runner/lib/src/options.dart

@@ -1005,7 +1005,6 @@ void listConfigurations(Map<String, dynamic> options) {
 }
 
 /// Throws an [OptionParseException] with [message].
-// ignore: sdk_version_never
 Never _fail(String message) {
   throw OptionParseException(message);
 }

pkg/test_runner/lib/src/static_error.dart

@@ -702,8 +702,6 @@ class _ErrorExpectationParser {
     return line;
   }
 
-  // TODO(athom): remove when migrated to null safety.
-  // ignore: sdk_version_never
   Never _fail(String message) {
     throw FormatException("Test error on line ${_currentLine + 1}: $message");
   }