Get rid of almost all uses of these definitions. They're still defined for
delinquent out-of-tree drivers, and also for the Mesa build. As well as
for miinitext.c. But largely gone.
Dist helper shell scripts.
Dist XAA.HOWTO and a few more unused C files.
Dist xorgconf.cpp.
Fix DIST_EXTRA typo.
Clean yacc and lex generated files only during make maintainer-clean as we
don't expect users to have those tools installed.