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/p2p/BUILD.gn b/p2p/BUILD.gn
index 473281a..a2f5160 100644
--- a/p2p/BUILD.gn
+++ b/p2p/BUILD.gn
@@ -91,6 +91,7 @@
     "../rtc_base:safe_minmax",
     "../rtc_base:stringutils",
     "../system_wrappers:field_trial_api",
+    "//third_party/abseil-cpp/absl/memory",
     "//third_party/abseil-cpp/absl/types:optional",
   ]
 
@@ -138,6 +139,7 @@
       "../rtc_base:rtc_base_approved",
       "../rtc_base:rtc_base_tests_utils",
       "../test:test_support",
+      "//third_party/abseil-cpp/absl/memory",
     ]
   }
 
@@ -178,6 +180,7 @@
       "../rtc_base:stringutils",
       "../test:test_support",
       "//testing/gtest",
+      "//third_party/abseil-cpp/absl/memory",
     ]
     if (!build_with_chromium && is_clang) {
       # Suppress warnings from the Chromium Clang plugin (bugs.webrtc.org/163).