Revert "wifi: rtl8xxxu: enable MFP support"

This reverts commit 77f5924f.

There is a more elegant solution to check for not decrypted frames,
which is to check the security flag in the RX descriptor.

Revert commit 77f5924f

 ("wifi: rtl8xxxu: enable MFP support") in
favor of this to be able to send it to stable.

Signed-off-by: Martin Kaistra <martin.kaistra@linutronix.de>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://msgid.link/20240418071813.1883174-2-martin.kaistra@linutronix.de