action: disallow setting an action_field default for all types

action: disallow setting an action_field default for all types

Currently where it is possible to write:
    setMods.clearLocks = True;
It's also possible to write:
    action.clearLocks = True;
This will set the default value for the clearLocks action field for
*all* action types, as opposed to just setMods in this case. If
subsequently an action is used for which this field does not make sense,
it will error out.
This doesn't make any sense, because any given field is only possible by at
most 3 or 4 action types... which you might as well write explicitly and
avoid the side effect mentioned above.
Needless to say this is one of xkbcomp's "hidden features" and is not
used anywhere; remove it.

Signed-off-by: Ran Benita <ran234@gmail.com>