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/rtc_base/BUILD.gn b/rtc_base/BUILD.gn
index 716d0b2..533eed8 100644
--- a/rtc_base/BUILD.gn
+++ b/rtc_base/BUILD.gn
@@ -533,6 +533,7 @@
   deps = [
     ":macromagic",
     ":ptr_util",
+    "//third_party/abseil-cpp/absl/memory",
   ]
 }
 
@@ -727,6 +728,7 @@
     ":stringutils",
     "..:webrtc_common",
     "../api:array_view",
+    "//third_party/abseil-cpp/absl/memory",
     "//third_party/abseil-cpp/absl/types:optional",
   ]
   public_deps = [
@@ -1036,6 +1038,7 @@
     "../test:field_trial",
     "../test:test_support",
     "system:fallthrough",
+    "//third_party/abseil-cpp/absl/memory",
   ]
   public_deps = [
     "//testing/gtest",
@@ -1100,6 +1103,7 @@
       "../test:fileutils",
       "../test:test_support",
       "//testing/gtest",
+      "//third_party/abseil-cpp/absl/memory",
     ]
     if (is_win) {
       sources += [ "win32socketserver_unittest.cc" ]
@@ -1178,6 +1182,7 @@
       "../test:fileutils",
       "../test:test_support",
       "memory:unittests",
+      "//third_party/abseil-cpp/absl/memory",
     ]
   }
 
@@ -1303,6 +1308,7 @@
       "../api:array_view",
       "../test:fileutils",
       "../test:test_support",
+      "//third_party/abseil-cpp/absl/memory",
       "//third_party/abseil-cpp/absl/types:optional",
     ]
     public_deps = [