Remove maintainer comment from Emacs 28 module snippet.

This is the same as 44c13eefe8 on
master.  We should also remove this comment on the release branch,
otherwise it ends up in the emacs-module.h shipped to users.

* src/module-env-28.h: Remove maintainer comment.

src/module-env-28.h

@@ -1,7 +1,3 @@
-  /* Add module environment functions newly added in Emacs 28 here.
-     Before Emacs 28 is released, remove this comment and start
-     module-env-29.h on the master branch.  */
-
   void (*(*EMACS_ATTRIBUTE_NONNULL (1)
             get_function_finalizer) (emacs_env *env,
                                      emacs_value arg)) (void *) EMACS_NOEXCEPT;