Update to xorg-util-macros-1.7.0.

1.7.0:
config: remove the xorg-macros pc.in file from EXTRA_DIST
doc: add XORG_CHECK_SGML_DOCTOOLS to detect xorg-sgml-doctools

1.6.0:
All document generation macros are now available.

1.5.0:
There are 3 new macros to help modules manage if/when docs get build in
a consistent way.

1.4.2:
Two behaviour changes in this minor release:
- XORG_INSTALL looks for the INSTALL file in $datadir/util-macros/
  instead of $docdir
- XORG_CHECK_MALLOC_ZERO doesn't abort when cross-compiling even without
  an explicit --{en,dis}able-malloc0returnsnull

(tnn)