[messages] Remove GeneratedDiagnosticFile.shouldUseExplicitNewOrConst.

Now that scanner errors are generated to `package:analyzer` rather
than `package:_fe_analyzer_shared` (see
https://dart-review.googlesource.com/c/sdk/+/455263), there is no
`GeneratedDiagnosticFile` for which this value is `true`, so it can
safely be hardcoded to `false`.

Change-Id: I6a6a6964c6d9f683bb0627719b90076eb041f74c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/461142
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>

Author: stereotype441

pkg/analyzer_utilities/lib/analyzer_messages.dart

@@ -588,13 +588,10 @@ mixin MessageWithAnalyzerCode on Message {
       var templateParameters =
           '<LocatableDiagnostic Function({$withArgumentsParams})>';
       staticType = 'DiagnosticWithArguments$templateParameters';
-      var newIfNeeded = diagnosticClassInfo.file.shouldUseExplicitNewOrConst
-          ? 'new '
-          : '';
       memberAccumulator.staticMethods[withArgumentsName] =
           '''
 static LocatableDiagnostic $withArgumentsName({$withArgumentsParams}) {
-  return ${newIfNeeded}LocatableDiagnosticImpl(
+  return LocatableDiagnosticImpl(
     ${diagnosticClassInfo.name}.$constantName, [$argumentNames]);
 }''';
     } else {
@@ -606,9 +603,6 @@ static LocatableDiagnostic $withArgumentsName({$withArgumentsParams}) {
     var constant = StringBuffer();
     outputConstantHeader(constant);
     constant.writeln('  static const $staticType $constantName =');
-    if (diagnosticClassInfo.file.shouldUseExplicitNewOrConst) {
-      constant.writeln('const ');
-    }
     constant.writeln('$concreteClassName(');
     constant.writeln(
       'name: ${sharedNameReference ?? "'${sharedName ?? diagnosticCode}'"},',

pkg/analyzer_utilities/lib/messages.dart

@@ -516,16 +516,11 @@ class GeneratedDiagnosticFile {
   /// The URI of the library that the generated file will be a part of.
   final String parentLibrary;
 
-  /// Whether the generated file should use the `new` and `const` keywords when
-  /// generating constructor invocations.
-  final bool shouldUseExplicitNewOrConst;
-
   final bool shouldIgnorePreferSingleQuotes;
 
   const GeneratedDiagnosticFile({
     required this.path,
     required this.parentLibrary,
-    this.shouldUseExplicitNewOrConst = false,
     this.shouldIgnorePreferSingleQuotes = false,
   });
 }