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/compiler/oat_writer.cc b/compiler/oat_writer.cc
index a78a5b3..640698b 100644
--- a/compiler/oat_writer.cc
+++ b/compiler/oat_writer.cc
@@ -39,6 +39,7 @@
 #include "mirror/class_loader.h"
 #include "mirror/dex_cache-inl.h"
 #include "mirror/object-inl.h"
+#include "oat_quick_method_header.h"
 #include "os.h"
 #include "output_stream.h"
 #include "safe_map.h"