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/gc/space/malloc_space.cc b/runtime/gc/space/malloc_space.cc
index ba46dcc..e710409 100644
--- a/runtime/gc/space/malloc_space.cc
+++ b/runtime/gc/space/malloc_space.cc
@@ -188,7 +188,7 @@
   VLOG(heap) << "Capacity " << PrettySize(capacity);
   // Remap the tail.
   std::string error_msg;
-  UniquePtr<MemMap> mem_map(GetMemMap()->RemapAtEnd(end_, alloc_space_name,
+  std::unique_ptr<MemMap> mem_map(GetMemMap()->RemapAtEnd(end_, alloc_space_name,
                                                     PROT_READ | PROT_WRITE, &error_msg));
   CHECK(mem_map.get() != nullptr) << error_msg;
   void* allocator = CreateAllocator(end_, starting_size_, initial_size_, capacity, low_memory_mode);