Use libunwindstack instead of libbacktrace.

Replace all instances of libbacktrace code with equivalent
libunwindstack code.

Test: Run 037-cfi test in optimized, interpreter, jit modes.
Test: Ran 004-ThreadStress in a loop for optimized, interpreter, jit modes.
Test: Forced an ANR and verified native stacks are correct, and that
Test: native stacks correctly stop before java stacks.
Change-Id: I642ffd61b731dae6a68a5ba9453485a79f608d28
diff --git a/runtime/runtime_common.h b/runtime/runtime_common.h
index 925594e..ec08907 100644
--- a/runtime/runtime_common.h
+++ b/runtime/runtime_common.h
@@ -42,7 +42,7 @@
   void Dump(std::ostream& os) const {
     // This is a backtrace from a crash, do not skip any frames in case the
     // crash is in the unwinder itself.
-    DumpNativeStack(os, GetTid(), nullptr, "\t", nullptr, raw_context_, false);
+    DumpNativeStack(os, GetTid(), "\t", nullptr, raw_context_, false);
   }
  private:
   // Stores the context of the signal that was unexpected and will terminate the runtime. The