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/test/466-get-live-vreg/get_live_vreg_jni.cc b/test/466-get-live-vreg/get_live_vreg_jni.cc
index 2a56a7f..375a3fc 100644
--- a/test/466-get-live-vreg/get_live_vreg_jni.cc
+++ b/test/466-get-live-vreg/get_live_vreg_jni.cc
@@ -15,9 +15,9 @@
  */
 
 #include "arch/context.h"
-#include "art_code.h"
 #include "art_method-inl.h"
 #include "jni.h"
+#include "oat_quick_method_header.h"
 #include "scoped_thread_state_change.h"
 #include "stack.h"
 #include "thread.h"
@@ -44,7 +44,7 @@
       found_method_ = true;
       uint32_t value = 0;
       if (GetCurrentQuickFrame() != nullptr &&
-          GetCurrentCode().IsOptimized(sizeof(void*)) &&
+          GetCurrentOatQuickMethodHeader()->IsOptimized() &&
           !Runtime::Current()->IsDebuggable()) {
         CHECK_EQ(GetVReg(m, 0, kIntVReg, &value), false);
       } else {