Remove unnecessary this. qualifiers. (#166805)

I'm fixing a bug in a lint, and fixing existing violations.
https://dart-review.googlesource.com/c/sdk/+/421421



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packages/flutter/lib/src/cupertino/route.dart

@@ -345,7 +345,7 @@ class _PageBasedCupertinoPageRoute<T> extends PageRoute<T> with CupertinoRouteTr
 
   @override
   DelegatedTransitionBuilder? get delegatedTransition =>
-      this.fullscreenDialog ? null : CupertinoPageTransition.delegatedTransition;
+      fullscreenDialog ? null : CupertinoPageTransition.delegatedTransition;
 
   CupertinoPage<T> get _page => settings as CupertinoPage<T>;
 

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

@@ -2134,7 +2134,7 @@ abstract class ModalRoute<T> extends TransitionRoute<T> with LocalHistoryRoute<T
   void didChangeNext(Route<dynamic>? nextRoute) {
     if (nextRoute is ModalRoute<T> &&
         canTransitionTo(nextRoute) &&
-        nextRoute.delegatedTransition != this.delegatedTransition) {
+        nextRoute.delegatedTransition != delegatedTransition) {
       receivedTransition = nextRoute.delegatedTransition;
     } else {
       receivedTransition = null;
@@ -2147,7 +2147,7 @@ abstract class ModalRoute<T> extends TransitionRoute<T> with LocalHistoryRoute<T
   void didPopNext(Route<dynamic> nextRoute) {
     if (nextRoute is ModalRoute<T> &&
         canTransitionTo(nextRoute) &&
-        nextRoute.delegatedTransition != this.delegatedTransition) {
+        nextRoute.delegatedTransition != delegatedTransition) {
       receivedTransition = nextRoute.delegatedTransition;
     } else {
       receivedTransition = null;