Doc: drop support for docbook-xsl before 1.73.0
Drop the DOCBOOK_XSL_172 config knob, which was needed with docbook-xsl
1.72 (but neither 1.71 nor 1.73). Version 1.73.0 is more than twelve
years old.
Together with the last few commits, we are now at a point where we don't
have any Makefile knobs to cater to old/broken versions of docbook-xsl.
Signed-off-by: Martin Ågren <martin.agren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
authored by