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/compiler/compilers.h b/compiler/compilers.h
index e523d64..2c231e1 100644
--- a/compiler/compilers.h
+++ b/compiler/compilers.h
@@ -92,7 +92,7 @@
                              const DexFile& dex_file) const;
 
  private:
-  UniquePtr<std::ostream> visualizer_output_;
+  std::unique_ptr<std::ostream> visualizer_output_;
 
   DISALLOW_COPY_AND_ASSIGN(OptimizingCompiler);
 };