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..89c1c88c45b597ac25f4c5546304e7b9015c0bd0 100644
--- a/webrtc/modules/rtp_rtcp/BUILD.gn
+++ b/webrtc/modules/rtp_rtcp/BUILD.gn
@@ -33,6 +33,8 @@ rtc_static_library("rtp_rtcp") {
     "source/forward_error_correction.h",
     "source/forward_error_correction_internal.cc",
     "source/forward_error_correction_internal.h",
+    "source/nack_stats.cc",
+    "source/nack_stats.h",
     "source/packet_loss_stats.cc",
     "source/packet_loss_stats.h",
     "source/playout_delay_oracle.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",
@@ -238,6 +238,7 @@ if (rtc_include_tests) {
       "source/flexfec_receiver_unittest.cc",
       "source/flexfec_sender_unittest.cc",
       "source/nack_rtx_unittest.cc",
+      "source/nack_stats_unittest.cc",
       "source/packet_loss_stats_unittest.cc",
       "source/playout_delay_oracle_unittest.cc",
       "source/receive_statistics_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",