ath9k_hw: remove initvals for hardware which was never sold

According to documentation, The following chip revisions were never sold:

- AR9280 v1.0
- AR9285 v1.0
- AR9285 v1.1
- AR9287 v1.0

Removing initvals specific to these chip revisions saves around 30k in
binary size (tested on MIPS).

Signed-off-by: Felix Fietkau <nbd@openwrt.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>