Delete remaining usage of RtpHeaderParser test helper.

Bug: None
Change-Id: Ia4f8c5dc212f25b1a507e13955973ce4aa6a7ddc
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/225550
Reviewed-by: Niels Moller <nisse@webrtc.org>
Reviewed-by: Björn Terelius <terelius@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34525}

modules/rtp_rtcp/source/rtp_rtcp_impl_unittest.cc

@@ -24,7 +24,6 @@
 #include "test/gmock.h"
 #include "test/gtest.h"
 #include "test/rtcp_packet_parser.h"
-#include "test/rtp_header_parser.h"
 
 using ::testing::ElementsAre;
 using ::testing::Eq;