staging: r8188eu: btcoex_rfon is always false

btcoex_rfon is always false in this driver. Remove the variable and code
that will never be executed.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20210911141521.24901-2-martin@kaiser.cx


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