ath10k: remove duplicate and unused rx rate flags

All these flags are not used and their use is completely
covered by 'ath10k_hw_rate_ofdm', 'ath10k_hw_rate_cck',
and RX_PPDU_START_RATE_FLAG

Signed-off-by: Mohammed Shafi Shajakhan <mohammed@qti.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>