ice: remove unused aggregator node functions

With the introduction of ice_cfg_vsi_agg(), the ice_cfg_agg() and
ice_move_vsi_to_agg() functions are no longer used. Remove them.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>