Revert async changes.

runtime/vm/raw_object.h

Index: runtime/vm/raw_object.h
diff --git a/runtime/vm/raw_object.h b/runtime/vm/raw_object.h
index 1123ff620eeb2e9a7c7681688aad8d6ed5280f70..cf3ca12bac6b3ef002f9c1fee59d729f16515043 100644
--- a/runtime/vm/raw_object.h
+++ b/runtime/vm/raw_object.h
@@ -615,11 +615,6 @@ class RawFunction : public RawObject {
     kInvokeFieldDispatcher,  // invokes a field as a closure.
   };
 
-  enum AsyncModifier {
-    kNoModifier,
-    kAsync,
-  };
-
  private:
   // So that the MarkingVisitor::DetachCode can null out the code fields.
   friend class MarkingVisitor;
@@ -655,7 +650,7 @@ class RawFunction : public RawObject {
   int16_t num_fixed_parameters_;
   int16_t num_optional_parameters_;  // > 0: positional; < 0: named.
   int16_t deoptimization_counter_;
-  uint32_t kind_tag_;  // See Function::KindTagBits.
+  uint16_t kind_tag_;  // See Function::KindTagBits.
   uint16_t optimized_instruction_count_;
   uint16_t optimized_call_site_count_;
 };