[Cleanup] Add missing #include. Remove useless ones.

This CL is the result of running include-what-you-use tool on part
of the code base (audio target and dependencies) plus manual fixes.

bug: webrtc:8311
Change-Id: I277d281ce943c3ecc1bd45fd8d83055931743604
Reviewed-on: https://webrtc-review.googlesource.com/c/106280
Commit-Queue: Yves Gerey <yvesg@google.com>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25311}
diff --git a/rtc_base/nethelpers.h b/rtc_base/nethelpers.h
index 429f0c0..138f958 100644
--- a/rtc_base/nethelpers.h
+++ b/rtc_base/nethelpers.h
@@ -12,8 +12,7 @@
 #define RTC_BASE_NETHELPERS_H_
 
 #if defined(WEBRTC_POSIX)
-#include <netdb.h>
-#include <stddef.h>
+#include <sys/socket.h>
 #elif WEBRTC_WIN
 #include <winsock2.h>  // NOLINT
 #endif
@@ -21,7 +20,7 @@
 #include <vector>
 
 #include "rtc_base/asyncresolverinterface.h"
-#include "rtc_base/ipaddress.h"  // for IPAddress
+#include "rtc_base/ipaddress.h"
 #include "rtc_base/signalthread.h"
 #include "rtc_base/socketaddress.h"