Removing obsolete comment.

While the original purpose of introducing `$Msg$::_Internal` is fulfilled,
this per-message `_Internal` type is still useful. This CL removes obsolete
TODO. We will keep this for a while.

PiperOrigin-RevId: 906521353

src/google/protobuf/compiler/cpp/message.cc

diff --git a/src/google/protobuf/compiler/cpp/message.cc b/src/google/protobuf/compiler/cpp/message.cc
index 351fc46..cd0768c 100644
--- a/src/google/protobuf/compiler/cpp/message.cc
+++ b/src/google/protobuf/compiler/cpp/message.cc
@@ -2286,8 +2286,6 @@
           // @@protoc_insertion_point(class_scope:$full_name$)
           //~ Generate private members.
          private:
-          //~ TODO: Remove hack to track field access and remove
-          //~ this class.
           class _Internal;
           $decl_set_has$;
           $decl_oneof_has$;