[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}

modules/audio_coding/neteq/rtcp.cc

@@ -10,10 +10,12 @@
 
 #include "modules/audio_coding/neteq/rtcp.h"
 
-#include <stdlib.h>
-#include <string.h>
-
 #include <algorithm>
+#include <cstdlib>
+
+#include "api/rtp_headers.h"
+#include "common_types.h"
+#include "rtc_base/checks.h"
 
 namespace webrtc {