wifi: rtw89: disable firmware training HE GI and LTF

Given the performance trade-off associated with firmware training
HE GI/LTF, especially in high attenuation environments, we have
decided to utilize a constant value instead.

Signed-off-by: Kuan-Chung Chen <damon.chen@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20241206055716.18598-5-pkshih@realtek.com