Revert of skstd -> std for unique_ptr

include/core/SkRefCnt.h

Index: include/core/SkRefCnt.h
diff --git a/include/core/SkRefCnt.h b/include/core/SkRefCnt.h
index abe3fb28278206147693753a5137c40f36e0a4f3..0e8d857722d2678d8620fe923267fff82b7e197e 100644
--- a/include/core/SkRefCnt.h
+++ b/include/core/SkRefCnt.h
@@ -9,8 +9,8 @@
 #define SkRefCnt_DEFINED
 
 #include "../private/SkAtomics.h"
+#include "../private/SkUniquePtr.h"
 #include "SkTypes.h"
-#include <memory>
 
 /** \class SkRefCntBase
 
@@ -185,15 +185,12 @@
 /**
  *  Utility class that simply unref's its argument in the destructor.
  */
-template <typename T> class SkAutoTUnref : public std::unique_ptr<T, SkTUnref<T>> {
-public:
-    explicit SkAutoTUnref(T* obj = nullptr) : std::unique_ptr<T, SkTUnref<T>>(obj) {}
+template <typename T> class SkAutoTUnref : public skstd::unique_ptr<T, SkTUnref<T>> {
+public:
+    explicit SkAutoTUnref(T* obj = nullptr) : skstd::unique_ptr<T, SkTUnref<T>>(obj) {}
 
     T* detach() { return this->release(); }
     operator T*() const { return this->get(); }
-
-    // unique_ptr's operator bool() is not always be explicit on Android.  Make sure this is.
-    explicit operator bool() const { return this->get() != nullptr; }
 };
 // Can't use the #define trick below to guard a bare SkAutoTUnref(...) because it's templated. :(