Delete AsyncSocket class, merge into Socket class

Bug: webrtc:13065
Change-Id: I13afee2386ea9c4de0e4fa95133f0c4d3ec826e8
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/227031
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34787}
diff --git a/rtc_base/nat_server.cc b/rtc_base/nat_server.cc
index 725a57b..b818685 100644
--- a/rtc_base/nat_server.cc
+++ b/rtc_base/nat_server.cc
@@ -70,7 +70,7 @@
 // a TCP connection to the NAT server.
 class NATProxyServerSocket : public AsyncProxyServerSocket {
  public:
-  NATProxyServerSocket(AsyncSocket* socket)
+  NATProxyServerSocket(Socket* socket)
       : AsyncProxyServerSocket(socket, kNATEncodedIPv6AddressSize) {
     BufferInput(true);
   }
@@ -119,7 +119,7 @@
       : ProxyServer(int_factory, int_addr, ext_factory, ext_ip) {}
 
  protected:
-  AsyncProxyServerSocket* WrapSocket(AsyncSocket* socket) override {
+  AsyncProxyServerSocket* WrapSocket(Socket* socket) override {
     return new NATProxyServerSocket(socket);
   }
 };