mac80211: more kernel-doc fixes

Fix (delete) more mac80211 kernel-doc:

Warning(linux-2.6.28-git13//include/net/mac80211.h:375): Excess struct/union/enum/typedef member 'retry_count' description in 'ieee80211_tx_info'
Warning(linux-2.6.28-git13//net/mac80211/sta_info.h:308): Excess struct/union/enum/typedef member 'last_txrate' description in 'sta_info'

Signed-off-by: Randy Dunlap <[e-mail]>
Signed-off-by: John W. Linville <[e-mail]>

include/net/mac80211.h

···
  * @control: union for control data
  * @status: union for status data
  * @driver_data: array of driver_data pointers
- * @retry_count: number of retries
  * @ampdu_ack_len: number of aggregated frames.
  * 	relevant only if IEEE80211_TX_STATUS_AMPDU was set.
  * @ampdu_ack_map: block ack bit map for the aggregation.

net/mac80211/sta_info.h

···
  * @tx_packets: number of RX/TX MSDUs
  * @tx_bytes: number of bytes transmitted to this STA
  * @tx_fragments: number of transmitted MPDUs
- * @last_txrate: description of the last used transmit rate
  * @tid_seq: per-TID sequence numbers for sending to this STA
  * @ampdu_mlme: A-MPDU state machine state
  * @timer_to_tid: identity mapping to ID timers