Revert "Improvements to causal async stack traces"

runtime/vm/debugger.h

Index: runtime/vm/debugger.h
diff --git a/runtime/vm/debugger.h b/runtime/vm/debugger.h
index bf932feb31e18e883c1f587416453068f129b081..20af85cbdaf8f17a0d80a5a5b60eb7de81626f03 100644
--- a/runtime/vm/debugger.h
+++ b/runtime/vm/debugger.h
@@ -349,11 +349,11 @@ class ActivationFrame : public ZoneAllocated {
   static const char* KindToCString(Kind kind) {
     switch (kind) {
       case kRegular:
-        return "Regular";
+        return "kRegular";
       case kAsyncCausal:
-        return "AsyncCausal";
+        return "kAsyncCausal";
       case kAsyncSuspensionMarker:
-        return "AsyncSuspensionMarker";
+        return "kAsyncSuspensionMarker";
       default:
         UNREACHABLE();
         return "";