wifi: ath9k: delete some unused/duplicate macros

The rate macros are for AR9002 and not correct for AR9003.

The AGC 3 macros are unused and have incorrect values, at least for
QCN5502, where AR_AGC3_BASE should be 0x2de00.

This change does not appear to affect the final binary.

Signed-off-by: Wenli Looi <wlooi@ucalgary.ca>
Acked-by: Toke Høiland-Jørgensen <toke@toke.dk>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://msgid.link/20230629231625.951744-3-wlooi@ucalgary.ca