staging: wfx: drop module version

wfx_version.h says that this code is same same than driver 2.3.1 hosted
on github:

    https://github.com/siliconlabs/wfx-linux-driver/tree/2.3.1-public



However, it is inaccurate, driver in-tree contains multiple small
patches ahead 2.3.1.

I prefer to drop this confusing information.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20191017093954.657-1-Jerome.Pouiller@silabs.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>