rt2x00: Remove STATE_RADIO_IRQ_OFF_ISR and STATE_RADIO_IRQ_ON_ISR

Remove STATE_RADIO_IRQ_OFF_ISR and STATE_RADIO_IRQ_ON_ISR as they are
not used anymore.

Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
Acked-by: Gertjan van Wingerde <gwingerde@gmail.com>
Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>