README: remove "for now" qualifier on ejabberd requirements

[rozzin]

This creates a lot of ambiguity around when "now" actually is or was, whether it's `still true', etc. And it leads people to waste both their own time and others' trying to determine whether those changes have been integrated into the mainline ejabberd in the intervening years between when the "for now" statement was first made and the release of ejabberd that they're running, or whether the statement is still actually current (which it is).