[m-rev.] trivial diff: delete an out-of-date XXX comment

[Julien Fischer]

Delete an out-of-date XXX comment.

library/builtin.m:
     Delete the XXX comment about reporting an error for attempts to redefine
     builtin types.  The compiler now does this.

Julien.

diff --git a/library/builtin.m b/library/builtin.m
index 410daa4..e5c013c 100644
--- a/library/builtin.m
+++ b/library/builtin.m
@@ -30,9 +30,7 @@
  % and tuple types `{}', `{T}', `{T1, T2}', ...
  % and the types `pred', `pred(T)', `pred(T1, T2)', `pred(T1, T2, T3)', ...
  % and `func(T1) = T2', `func(T1, T2) = T3', `func(T1, T2, T3) = T4', ...
-% are builtin and are implemented using special code in the
-% type-checker. (XXX TODO: report an error for attempts to redefine
-% these types.)
+% are builtin and are implemented using special code in the type-checker.

      % The type c_pointer can be used by predicates that use the
      % C interface.