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}
diff --git a/api/audio_codecs/opus/audio_decoder_opus.cc b/api/audio_codecs/opus/audio_decoder_opus.cc
index 81bee77..41397f0 100644
--- a/api/audio_codecs/opus/audio_decoder_opus.cc
+++ b/api/audio_codecs/opus/audio_decoder_opus.cc
@@ -14,9 +14,9 @@
 #include <utility>
 #include <vector>
 
+#include "absl/memory/memory.h"
 #include "common_types.h"  // NOLINT(build/include)
 #include "modules/audio_coding/codecs/opus/audio_decoder_opus.h"
-#include "rtc_base/ptr_util.h"
 
 namespace webrtc {
 
@@ -57,7 +57,7 @@
 std::unique_ptr<AudioDecoder> AudioDecoderOpus::MakeAudioDecoder(
     Config config,
     absl::optional<AudioCodecPairId> /*codec_pair_id*/) {
-  return rtc::MakeUnique<AudioDecoderOpusImpl>(config.num_channels);
+  return absl::make_unique<AudioDecoderOpusImpl>(config.num_channels);
 }
 
 }  // namespace webrtc