gnu: Consistently use modular xorg source URIs in xorg.scm.
* gnu/packages/xorg.scm (bigreqsproto, compositeproto, damageproto)
(dmxproto, encodings, font-adobe100dpi, font-adobe75dpi, font-alias)
(font-arabic-misc, font-cronyx-cyrillic, font-dec-misc, font-isas-misc)
(font-micro-misc, font-misc-cyrillic, font-misc-ethiopic, font-misc-misc)
(font-mutt-misc, font-schumacher-misc, font-screen-cyrillic, font-sony-misc)
(font-sun-misc, font-util, font-winitzki-cyrillic, font-xfree86-type1)
(libpthread-stubs, libwindowswm, libxdmcp, libxkbfile, libxscrnsaver)
(luit, recordproto, renderproto, resourceproto, scrnsaverproto, setxkbmap)
(smproxy, windowswmproto, x11perf, xcb-proto, xcmiscproto, xcmsdb, xdriinfo)
(xf86-input-void, xf86-video-newport, xf86bigfontproto, xf86dgaproto)
(xf86driproto, xf86vidmodeproto, xgamma, xineramaproto, xkbevd, xlsatoms)
(xorg-sgml-doctools, xpr, xwud, fixesproto, mkfontdir, libxcb, xcb-util)
(xcb-util-image, xcb-util-keysyms, xcb-util-renderutil, kbproto, xbitmaps):
Use source URIs with prefix mirror://xorg/individual/ for consistency.
(dri3proto, presentproto, printproto): Remove comments about them not
being part of X11R7.7.
d2611ffbb5