Shrink struct rmatt_event_data.

Shrink struct rmatt_event_data.

The aft event handler needs to know the bit number of the attribute which is
being removed in order to clear the bit in the afs info structure of each row
of the audio file table. The handler does not need to know the attribute's
name, though, and remove_attribute() already prints it, so remove this field
from the event data structure.