INSTALL: drop support for docbook-xsl before 1.74
Several of the previous commits have been bumping the minimum supported
version of docbook-xsl and dropping various workarounds. Most recently,
we made the minimum be 1.73.0.
In INSTALL, we claim that with 1.73, one needs a certain patch in
contrib/patches/. There is no such patch. It was added in
2ec39edad9
("INSTALL: add warning on docbook-xsl 1.72 and 1.73", 2007-08-03) and
dropped in
9721ac9010 ("contrib: remove continuous/ and patches/",
2013-06-03).
Rather than resurrecting version 1.73 and the patch and testing them,
just raise our minimum supported docbook-xsl version to 1.74.
Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>