Cleanup: Make AsyncResolveInterface::Start(addr,family) pure virtual

Dependencies have been updated now.

Bug: webrtc:14319, webrtc:14131
Change-Id: I03397f6dfa17cbb2faa85346c5ea37847f1e2482
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/271344
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Sameer Vijaykar <samvi@google.com>
Cr-Commit-Position: refs/heads/main@{#37944}
diff --git a/rtc_base/async_resolver_interface.h b/rtc_base/async_resolver_interface.h
index 998ebd8..829dc7e 100644
--- a/rtc_base/async_resolver_interface.h
+++ b/rtc_base/async_resolver_interface.h
@@ -27,11 +27,7 @@
   // Start address resolution of the hostname in `addr`.
   virtual void Start(const SocketAddress& addr) = 0;
   // Start address resolution of the hostname in `addr` matching `family`.
-  virtual void Start(const SocketAddress& addr, int family) {
-    // TODO(webrtc:14319) make pure virtual when all subclasses have been
-    // updated.
-    RTC_DCHECK_NOTREACHED();
-  }
+  virtual void Start(const SocketAddress& addr, int family) = 0;
   // Returns true iff the address from `Start` was successfully resolved.
   // If the address was successfully resolved, sets `addr` to a copy of the
   // address from `Start` with the IP address set to the top most resolved