Retire the 2.17 language feature experiment flags.

Remove them from tests.
(They should have been removed from tests before launcing 2.17.)

Change-Id: I546f6cb90fdf9e6ed1bb560f3715f9db163b7c68
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/250384
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Reviewed-by: Devon Carew <devoncarew@google.com>
Commit-Queue: Lasse Nielsen <lrn@google.com>

tools/experimental_features.yaml

@@ -233,6 +233,7 @@ features:
       void main() {
         T.t.test();
       }
+    expired: true
 
   named-arguments-anywhere:
     help: "Named Arguments Anywhere"
@@ -246,6 +247,7 @@ features:
       void main() {
         test(enabled : true, 'feature enabled');
       }
+    expired: true
 
   super-parameters:
     help: "Super-Initializer Parameters"
@@ -261,6 +263,7 @@ features:
       void main(){
         print(C('feature enabled').foo);
       }
+    expired: true
 
   inference-update-1:
     help: "Horizontal type inference for function expressions passed to generic invocations."