Update links to old linter site to dart.dev (#129866)

Removes the remaining links to the old linter site, to the guaranteed dart.dev/lints redirect.

Contributes to https://github.com/dart-lang/linter/issues/4460 and dart-lang/site-www#4499

Author: parlough

packages/flutter/lib/src/widgets/routes.dart

@@ -1813,9 +1813,9 @@ abstract class PopupRoute<T> extends ModalRoute<T> {
 ///
 /// ## Type arguments
 ///
-/// When using more aggressive
-/// [lints](http://dart-lang.github.io/linter/lints/), in particular lints such
-/// as `always_specify_types`, the Dart analyzer will require that certain types
+/// When using more aggressive [lints](https://dart.dev/lints),
+/// in particular lints such as `always_specify_types`,
+/// the Dart analyzer will require that certain types
 /// be given with their type arguments. Since the [Route] class and its
 /// subclasses have a type argument, this includes the arguments passed to this
 /// class. Consider using `dynamic` to specify the entire class of routes rather

packages/flutter_tools/templates/app_shared/analysis_options.yaml.tmpl

@@ -16,8 +16,7 @@ linter:
   # The lint rules applied to this project can be customized in the
   # section below to disable rules from the `package:flutter_lints/flutter.yaml`
   # included above or to enable additional rules. A list of all available lints
-  # and their documentation is published at
-  # https://dart-lang.github.io/linter/lints/index.html.
+  # and their documentation is published at https://dart.dev/lints.
   #
   # Instead of disabling a lint rule for the entire project in the
   # section below, it can also be suppressed for a single line of code