[mojo] Remove a reference to mojo::Binding in the documentation

R=rockot@chromium.org

Change-Id: Iba556a1d642d1dc4fb78e6960af104861396f54e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2019364
Auto-Submit: Alexander Timin <altimin@chromium.org>
Commit-Queue: Ken Rockot <rockot@google.com>
Reviewed-by: Ken Rockot <rockot@google.com>
Cr-Commit-Position: refs/heads/master@{#734996}

mojo/public/cpp/system/README.md

@@ -480,14 +480,15 @@ message pipe handles as mojom interfaces. For example:
 // Process A
 mojo::OutgoingInvitation invitation;
 auto pipe = invitation->AttachMessagePipe("x");
-mojo::Binding<foo::mojom::Bar> binding(
+mojo::Receiver<foo::mojom::Bar> receiver(
     &bar_impl,
-    foo::mojom::BarRequest(std::move(pipe)));
+    mojo::PendingReceiver<foo::mojom::Bar>(std::move(pipe)));
 
 // Process B
 auto invitation = mojo::IncomingInvitation::Accept(...);
 auto pipe = invitation->ExtractMessagePipe("x");
-mojo::Remote<foo::mojom::Bar> bar(mojo::PendingRemote<foo::mojom::Bar>(std::move(pipe), 0));
+mojo::Remote<foo::mojom::Bar> bar(
+    mojo::PendingRemote<foo::mojom::Bar>(std::move(pipe), 0));
 
 // Will asynchronously invoke bar_impl.DoSomething() in process A.
 bar->DoSomething();