Rename CMessage -> Message, to make the change in https://github.com/protocolbuffers/upb/pull/617 work as intended.

The previous change did not have the desired effect, because the generated code uses the class named "Message" instead of "CMessage."

There was no real need to use the class "CMessage" instead of "Message."  The new name is simpler and will make the previous change work.

PiperOrigin-RevId: 449309343
diff --git a/python/map.c b/python/map.c
index 31799a3..a0ba2fe 100644
--- a/python/map.c
+++ b/python/map.c
@@ -72,8 +72,8 @@
   PyUpb_MapContainer* self = _self;
   Py_DECREF(self->arena);
   if (PyUpb_MapContainer_IsStub(self)) {
-    PyUpb_CMessage_CacheDelete(self->ptr.parent,
-                               PyUpb_MapContainer_GetField(self));
+    PyUpb_Message_CacheDelete(self->ptr.parent,
+                              PyUpb_MapContainer_GetField(self));
     Py_DECREF(self->ptr.parent);
   } else {
     PyUpb_ObjCache_Delete(self->ptr.map);
@@ -92,7 +92,7 @@
                                      PyObject* arena) {
   // We only create stubs when the parent is reified, by convention.  However
   // this is not an invariant: the parent could become reified at any time.
-  assert(PyUpb_CMessage_GetIfReified(parent) == NULL);
+  assert(PyUpb_Message_GetIfReified(parent) == NULL);
   PyTypeObject* cls = PyUpb_MapContainer_GetClass(f);
   PyUpb_MapContainer* map = (void*)PyType_GenericAlloc(cls, 0);
   map->arena = arena;
@@ -141,7 +141,7 @@
   map =
       upb_Map_New(arena, upb_FieldDef_CType(key_f), upb_FieldDef_CType(val_f));
   upb_MessageValue msgval = {.map_val = map};
-  PyUpb_CMessage_SetConcreteSubobj(self->ptr.parent, f, msgval);
+  PyUpb_Message_SetConcreteSubobj(self->ptr.parent, f, msgval);
   PyUpb_MapContainer_Reify((PyObject*)self, map);
   return map;
 }
@@ -284,8 +284,8 @@
   return (PyUpb_MapContainer*)_self;
 }
 
-int PyUpb_CMessage_InitMapAttributes(PyObject* map, PyObject* value,
-                                     const upb_FieldDef* f);
+int PyUpb_Message_InitMapAttributes(PyObject* map, PyObject* value,
+                                    const upb_FieldDef* f);
 
 static PyObject* PyUpb_MapContainer_MergeFrom(PyObject* _self, PyObject* _arg) {
   PyUpb_MapContainer* self = (PyUpb_MapContainer*)_self;
@@ -295,7 +295,7 @@
     return PyErr_Format(PyExc_AttributeError, "Merging of dict is not allowed");
   }
 
-  if (PyUpb_CMessage_InitMapAttributes(_self, _arg, f) < 0) {
+  if (PyUpb_Message_InitMapAttributes(_self, _arg, f) < 0) {
     return NULL;
   }