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/optimizing/codegen_test.cc b/compiler/optimizing/codegen_test.cc
index d40990e..7684bb1 100644
--- a/compiler/optimizing/codegen_test.cc
+++ b/compiler/optimizing/codegen_test.cc
@@ -42,7 +42,7 @@
 
  private:
   size_t size_;
-  UniquePtr<uint8_t[]> memory_;
+  std::unique_ptr<uint8_t[]> memory_;
 
   DISALLOW_COPY_AND_ASSIGN(InternalCodeAllocator);
 };