Use absl::make_unique and absl::WrapUnique directly

Instead of going through our wrappers in ptr_util.h.

This CL was generated by the following script:

  git grep -l ptr_util | xargs perl -pi -e 's,#include "rtc_base/ptr_util.h",#include "absl/memory/memory.h",'
  git grep -l MakeUnique | xargs perl -pi -e 's,\b(rtc::)?MakeUnique\b,absl::make_unique,g'
  git grep -l WrapUnique | xargs perl -pi -e 's,\b(rtc::)?WrapUnique\b,absl::WrapUnique,g'
  git checkout -- rtc_base/ptr_util{.h,_unittest.cc}
  git cl format

Followed by manually adding dependencies on
//third_party/abseil-cpp/absl/memory until `gn check` stopped
complaining.

Bug: webrtc:9473
Change-Id: I89ccd363f070479b8c431eb2c3d404a46eaacc1c
Reviewed-on: https://webrtc-review.googlesource.com/86600
Commit-Queue: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23850}

modules/rtp_rtcp/source/rtcp_transceiver_impl_unittest.cc

@@ -12,6 +12,7 @@
 
 #include <vector>
 
+#include "absl/memory/memory.h"
 #include "api/video/video_bitrate_allocation.h"
 #include "modules/rtp_rtcp/include/receive_statistics.h"
 #include "modules/rtp_rtcp/mocks/mock_rtcp_rtt_stats.h"
@@ -21,7 +22,6 @@
 #include "modules/rtp_rtcp/source/time_util.h"
 #include "rtc_base/event.h"
 #include "rtc_base/fakeclock.h"
-#include "rtc_base/ptr_util.h"
 #include "rtc_base/task_queue.h"
 #include "test/gmock.h"
 #include "test/gtest.h"