rt2x00usb: drop rt2x00usb_disable_radio() from rt2800usb_disable_radio()

I have here FRITZ!WLAN USB Stick N v2 / idVendor=057c, idProduct=8501
and every single of this requests ends up with:

|ieee80211 phy0: rt2x00usb_vendor_request: Error - Vendor Request 0x0c  failed for offset 0x0000 with error -32

I was browsing the the vedor code and I haven't seen such request so I
remove it with this patch. If I wasn't look enough or if this error is
expected then please excuse :)

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>