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/jit/jit_compiler.cc b/compiler/jit/jit_compiler.cc
index a45df95..fcbd483 100644
--- a/compiler/jit/jit_compiler.cc
+++ b/compiler/jit/jit_compiler.cc
@@ -30,6 +30,7 @@
 #include "jit/jit.h"
 #include "jit/jit_code_cache.h"
 #include "oat_file-inl.h"
+#include "oat_quick_method_header.h"
 #include "object_lock.h"
 #include "thread_list.h"
 #include "verifier/method_verifier-inl.h"