-DDEBUG in libwr forces LOG_DEBUG level in libwr/wrs-msg.c. This is
the desired behaviour, but we want it off by default now.

All other DEBUG symbols in Makefiles have no effect, so they are
removed to avoid tricking our developers in setting/unsetting them
and see no effect at all.

Signed-off-by: Alessandro Rubini <rubini@gnudd.com>