Remove ArtCode.

- Instead use OatQuickMethodHeader.
- Various cleanups now that we don't have all those
  ArtMethod -> ArtCode -> OatQuickMethodHeader indirections.

As a consequence of this cleanup, exception handling got a bit
faster.

ParserCombinators benchmark (exception intensive) on x64: (lower is better)
Before:
ParserCombinators(RunTime): 1062500.0 us.
After:
ParserCombinators(RunTime): 833000.0 us.

Change-Id: Idac917b6f1b0dc254ad68fb3781cd61bccadb0f3
diff --git a/runtime/quick/quick_method_frame_info.h b/runtime/quick/quick_method_frame_info.h
index 684d4da..71f8265 100644
--- a/runtime/quick/quick_method_frame_info.h
+++ b/runtime/quick/quick_method_frame_info.h
@@ -50,6 +50,10 @@
     return fp_spill_mask_;
   }
 
+  size_t GetReturnPcOffset() const {
+    return FrameSizeInBytes() - sizeof(void*);
+  }
+
  private:
   uint32_t frame_size_in_bytes_;
   uint32_t core_spill_mask_;