rt2x00: Remove RT30XX Kconfig variables.

Enabling of RT30xx devices via Kconfig variables was introduced when these
devices weren't properly supported yet.
Now that that they are properly supported and functional, we can remove these
Kconfig variables for RT30xx devices and simply enable them whenever rt2800pci
and/or rt2800usb is enabled.

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