staging: wfx: remove hack about tx_rate policies

staging: wfx: remove hack about tx_rate policies

Current code contains a weird hack to avoid switch from 54Mbps CTS to
1Mbps. However, we have not been able to reproduce the problem and
hardware team don't know any defect of this kind. So, it seems this hack
is no more necessary.

Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200401110405.80282-33-Jerome.Pouiller@silabs.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>