Fix Makefile for FDL version fix

[Roland McGrath]

Thanks.  Last time I asked somebody about "the canonical texinfo.tex" and
the trailing whitespace question, it came to an impasse.  That is, I wanted
to get the canonical file and not touch it at all, but we have the trailing
whitespace prohibition.  For some reason I can't recall, whoever it was
(Paul Eggert, I think, but I'm not sure) seemed to think it was intractable
to get the canonical texinfo.tex to drop the trailing whitespace.  I still
think we ought to be using the bit-identical canonical file, but now that
you've done this, it's probably better than the status quo ante.

Thanks,
Roland