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/linker/arm/relative_patcher_thumb2_test.cc b/compiler/linker/arm/relative_patcher_thumb2_test.cc
index 13f67e6..5515313 100644
--- a/compiler/linker/arm/relative_patcher_thumb2_test.cc
+++ b/compiler/linker/arm/relative_patcher_thumb2_test.cc
@@ -16,6 +16,7 @@
 
 #include "linker/relative_patcher_test.h"
 #include "linker/arm/relative_patcher_thumb2.h"
+#include "oat_quick_method_header.h"
 
 namespace art {
 namespace linker {