Remove rtcp_utility as mostly unused.

webrtc/modules/rtp_rtcp/BUILD.gn

Index: webrtc/modules/rtp_rtcp/BUILD.gn
diff --git a/webrtc/modules/rtp_rtcp/BUILD.gn b/webrtc/modules/rtp_rtcp/BUILD.gn
index b7166ef4590294e6e4ad6f4ce37a6df86c7302c5..da742c5480aeb3fb8279e3b753587fec764d10dc 100644
--- a/webrtc/modules/rtp_rtcp/BUILD.gn
+++ b/webrtc/modules/rtp_rtcp/BUILD.gn
@@ -40,6 +40,8 @@ rtc_static_library("rtp_rtcp") {
     "source/receive_statistics_impl.cc",
     "source/receive_statistics_impl.h",
     "source/remote_ntp_time_estimator.cc",
+    "source/rtcp_nack_stats.cc",
+    "source/rtcp_nack_stats.h",
     "source/rtcp_packet.cc",
     "source/rtcp_packet.h",
     "source/rtcp_packet/app.cc",
@@ -100,8 +102,6 @@ rtc_static_library("rtp_rtcp") {
     "source/rtcp_receiver.h",
     "source/rtcp_sender.cc",
     "source/rtcp_sender.h",
-    "source/rtcp_utility.cc",
-    "source/rtcp_utility.h",
     "source/rtp_format.cc",
     "source/rtp_format.h",
     "source/rtp_format_h264.cc",
@@ -242,6 +242,7 @@ if (rtc_include_tests) {
       "source/playout_delay_oracle_unittest.cc",
       "source/receive_statistics_unittest.cc",
       "source/remote_ntp_time_estimator_unittest.cc",
+      "source/rtcp_nack_stats_unittest.cc",
       "source/rtcp_packet/app_unittest.cc",
       "source/rtcp_packet/bye_unittest.cc",
       "source/rtcp_packet/common_header_unittest.cc",
@@ -269,7 +270,6 @@ if (rtc_include_tests) {
       "source/rtcp_packet_unittest.cc",
       "source/rtcp_receiver_unittest.cc",
       "source/rtcp_sender_unittest.cc",
-      "source/rtcp_utility_unittest.cc",
       "source/rtp_fec_unittest.cc",
       "source/rtp_format_h264_unittest.cc",
       "source/rtp_format_vp8_test_helper.cc",