Revert "MEDIUM: init: set default for fd_hard_limit via DEFAULT_MAXFD"

Revert "MEDIUM: init: set default for fd_hard_limit via DEFAULT_MAXFD"

This reverts the following commit:
  e3aefc50d8 ("MEDIUM: init: set default for fd_hard_limit via DEFAULT_MAXFD")

Lukas expressed some concerns about possible consequences of this change
so let's wait for a consensus to be found in mainline before we backport
anything (if at all), as we certainly don't want to change the behavior
after it's backported. No version was released with this patch, it's the
right moment to revert it. For reference, the discussion is here:

    https://www.mail-archive.com/haproxy@formilux.org/msg45098.html

Please note that if it were to be re-introduced later, it should be
applied along with a small fix that already references it.