rt2x00: Fix FIXME comments in rt61pci and rt73usb on Michael MIC.

Both rt61pci and rt73usb check the Michael MIC in hardware and strip the
Michael MIC from received frames. This is perfectly allowed by mac80211 as
long as this is properly reported to mac80211.
Both these drivers reported the Michael MIC handling properly to mac80211, but
still contained a FIXME comment on this, which is not needed to be handled, since
mac80211 doesn't really need the Michael MIC in this case.

Signed-off-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>