staging: wilc1000: remove mutex txq_cs and it's related codes

mutex txq_cs is never used in the driver. txq_cs, txq_critical_section and
txq_lock have same pointer so just delete them and it's related codes.

Signed-off-by: Glen Lee <glen.lee@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>