[tldoc] no more \write18

[Karl Berry]

I have updated all the documentation except Chinese (writing separately
to those folks) to remove the mentions of the \write18 option in the
installer [now removed] and the two paragraphs about \write18 in the
"Present" [now disabled] section.  I added
\begin{comment}...\end{comment} in the latter case.

Hopefully my editing and/or recompiling did not corrupt every
8-or-more-bit character in the tex and/or pdf and/or html.  Please check
if you have a chance.

http://tug.org/svn/texlive/trunk/Master/texmf/doc/texlive/
(may not be there for an hour or so, as I write this, I just did the
commit.)

k