Revert "Use the new DNS resolver API in PeerConnection"

This reverts commit acf8ccb3c9f001b0ed749aca52b2d436d66f9586.

Reason for revert: Speculative revert for https://ci.chromium.org/ui/p/chromium/builders/try/win10_chromium_x64_rel_ng/b8851745102358680592/overview.

Original change's description:
> Use the new DNS resolver API in PeerConnection
>
> Bug: webrtc:12598
> Change-Id: I5a14058e7f28c993ed927749df7357c715ba83fb
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/212961
> Reviewed-by: Niels Moller <nisse@webrtc.org>
> Commit-Queue: Harald Alvestrand <hta@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#33561}

# Not skipping CQ checks because original CL landed > 1 day ago.

TBR=hta@webrtc.org

Bug: webrtc:12598
Change-Id: Idc9853cb569849c49052f9cbd865614710fff979
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/213188
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#33591}
diff --git a/pc/peer_connection.h b/pc/peer_connection.h
index c49c541..98c5519 100644
--- a/pc/peer_connection.h
+++ b/pc/peer_connection.h
@@ -23,7 +23,6 @@
 
 #include "absl/types/optional.h"
 #include "api/adaptation/resource.h"
-#include "api/async_dns_resolver.h"
 #include "api/async_resolver_factory.h"
 #include "api/audio_options.h"
 #include "api/candidate.h"
@@ -636,8 +635,11 @@
   PeerConnectionInterface::RTCConfiguration configuration_
       RTC_GUARDED_BY(signaling_thread());
 
-  const std::unique_ptr<AsyncDnsResolverFactoryInterface>
-      async_dns_resolver_factory_;
+  // TODO(zstein): |async_resolver_factory_| can currently be nullptr if it
+  // is not injected. It should be required once chromium supplies it.
+  // This member variable is only used by JsepTransportController so we should
+  // consider moving ownership to there.
+  const std::unique_ptr<AsyncResolverFactory> async_resolver_factory_;
   std::unique_ptr<cricket::PortAllocator>
       port_allocator_;  // TODO(bugs.webrtc.org/9987): Accessed on both
                         // signaling and network thread.