Delete rtc::Bind

Bug: webrtc:11339
Change-Id: Id53d17bbf37a15f482e9eb9f8762d2000c772dcc
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/202250
Reviewed-by: Tommi <tommi@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33099}

rtc_base/callback_list_unittest.cc

@@ -11,7 +11,6 @@
 #include <type_traits>
 
 #include "api/function_view.h"
-#include "rtc_base/bind.h"
 #include "rtc_base/callback_list.h"
 #include "test/gtest.h"
 
@@ -209,8 +208,6 @@ TEST(CallbackList, MemberFunctionTest) {
 }
 
 // todo(glahiru): Add a test case to catch some error for Karl's first fix
-// todo(glahiru): Add a test for rtc::Bind
-// which used the following code in the Send
 
 TEST(CallbackList, RemoveOneReceiver) {
   int removal_tag[2];