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/reflection.cc b/runtime/reflection.cc
index cbd66a6..55d35d1 100644
--- a/runtime/reflection.cc
+++ b/runtime/reflection.cc
@@ -342,7 +342,7 @@
   uint32_t num_bytes_;
   uint32_t* arg_array_;
   uint32_t small_arg_array_[kSmallArgArraySize];
-  UniquePtr<uint32_t[]> large_arg_array_;
+  std::unique_ptr<uint32_t[]> large_arg_array_;
 };
 
 static void CheckMethodArguments(mirror::ArtMethod* m, uint32_t* args)