ice: Remove unused function prototype

Commit 7c710869 ("ice: Add handlers for VF netdevice operations")
seems to have inadvertently introduced a function prototype for
ice_set_vf_bw that isn't implemented. Remove it.

Fixes: 7c710869 ("ice: Add handlers for VF netdevice operations")

Signed-off-by: Anirudh Venkataramanan <anirudh.venkataramanan@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>