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/monitor.cc b/runtime/monitor.cc
index 53e4a6f..0beb651 100644
--- a/runtime/monitor.cc
+++ b/runtime/monitor.cc
@@ -623,7 +623,7 @@
   DCHECK(self != NULL);
   DCHECK(obj != NULL);
   // Allocate and acquire a new monitor.
-  UniquePtr<Monitor> m(new Monitor(self, owner, obj, hash_code));
+  std::unique_ptr<Monitor> m(new Monitor(self, owner, obj, hash_code));
   if (m->Install(self)) {
     if (owner != nullptr) {
       VLOG(monitor) << "monitor: thread" << owner->GetThreadId()