A few pieces of code were abusing this define for other purposes, which are
converted to #ifndef DEBUG instead. There should be no ABI consequences
to this change.
The rationale is that having the define in xorg-server.h also disables
assert() drivers, which is unexpected, and also difficult to avoid since
xorg-server.h is included in their config.h, and you can't put a #undef in
config.h. As for removing it from the server instead of moving it to an
internal header, we probably shouldn't have unnecessary assert()s in
critical server paths anyway, and if we do we could #define NDEBUG in the
specific cases needed.
