BA did it 7 years ago. Replaced them with Ozone generators (ionisers). The humidifiers had a nasty habit of leaking on Pax heads, and had a high failure rate so were replaced.
Virgin 744s had them for the flight deck only. They were removed about 4 years ago - the given reason being they were causing corrosion on the contacts of the switches on the overhead panel.
reason for deactivation is that the calcium in the water deposits itself in places where you dont want it.... like the switches in the fire handles. Could be a problem if you need to fire the bottles.
Have actually seen the corrosion on the back of the ovehead panel from a 747-400 due to condensation. The fire handle contacts were so badly corroded they didn't actually work......!