Now we have a proper C++ library, use std::unique_ptr.

Also remove the Android.libcxx.mk and other bits of stlport compatibility
mechanics.

Change-Id: Icdf7188ba3c79cdf5617672c1cfd0a68ae596a61
diff --git a/runtime/hprof/hprof.cc b/runtime/hprof/hprof.cc
index fc8b594..91f1718 100644
--- a/runtime/hprof/hprof.cc
+++ b/runtime/hprof/hprof.cc
@@ -475,7 +475,7 @@
         }
       }
 
-      UniquePtr<File> file(new File(out_fd, filename_));
+      std::unique_ptr<File> file(new File(out_fd, filename_));
       okay = file->WriteFully(header_data_ptr_, header_data_size_) &&
           file->WriteFully(body_data_ptr_, body_data_size_);
       if (!okay) {