MAJOR: mworker: remove deprecated "master-worker" global keyword

MAJOR: mworker: remove deprecated "master-worker" global keyword

This keyword, when alone, was already deprecated in 3.3 and marked
for removal in 3.5. Now using it results in an error message inviting
to start haproxy with -W or -Ws instead.

In addition, "master-worker exit-on-failure", which used to automatically
enable the master-worker mode, now doesn't set it and complains if used
without. -W/-Ws. A special case was made for config checks though (-c).

Also worth noting that "daemon" applies to master as well as max-reloads,
and will soon need to be adjusted.