Reduce ABOUT-NLS to just a hyperlink.

Reduce ABOUT-NLS to just a hyperlink.

The common way to distribute information, nowadays, is through the web,
not by including files in tarballs of packages.  Also, the current
contents of ABOUT-NLS is outdated.

Reported by Samuel Thibault in <https://savannah.gnu.org/bugs/?54809>.

* gettext-runtime/ABOUT-NLS: Replace text with a reference to the online
documentation.
* gettext-runtime/Makefile.am (MAKEINFO): Remove variable.
(all-local, ABOUT-NLS): Remove rules.
* gettext-tools/src/msginit.c (main): Point the user to the online documentation
instead of the ABOUT-NLS file.
* gettext-tools/doc/gettext.texi (Installing Localizations, Prerequisites,
Makefile): Don't mention ABOUT-NLS any more.
* gettext-tools/doc/gettextize.texi: Update description of ABOUT-NLS.
* gettext-tools/doc/FAQ.html: Refer to the online documentation instead of the
ABOUT-NLS file.
* README: Don't mention ABOUT-NLS any more.