Remove MethodHelper from the interpreter.

Use ShadowFrame to get the executing method to avoid a handle for the current
method.
Various associated bits of header file clean-up and removal of an unnecessary
use of MethodHelper in CompilerDriver.

Change-Id: I3b6f4413701e8fc6b0c58b0041a0dd15472bedaa
diff --git a/runtime/native_bridge_art_interface.cc b/runtime/native_bridge_art_interface.cc
index ffadfc6..1775468 100644
--- a/runtime/native_bridge_art_interface.cc
+++ b/runtime/native_bridge_art_interface.cc
@@ -28,10 +28,8 @@
 
 static const char* GetMethodShorty(JNIEnv* env, jmethodID mid) {
   ScopedObjectAccess soa(env);
-  StackHandleScope<1> scope(soa.Self());
   mirror::ArtMethod* m = soa.DecodeMethod(mid);
-  MethodHelper mh(scope.NewHandle(m));
-  return mh.GetShorty();
+  return m->GetShorty();
 }
 
 static uint32_t GetNativeMethodCount(JNIEnv* env, jclass clazz) {