staging: rtl8723bs: remove decl of unused static const variable in os_dep/ioctl_linux.c

staging: rtl8723bs: remove decl of unused static const variable in os_dep/ioctl_linux.c

fix following kernel test robot warning:

   At top level:
   drivers/staging/rtl8723bs/os_dep/ioctl_linux.c:36:27:
warning: 'iw_operation_mode' defined but not used
		[-Wunused-const-variable=]
      36 | static const char * const iw_operation_mode[] = {
         |                           ^~~~~~~~~~~~~~~~~

Signed-off-by: Fabio Aiuto <fabioaiuto83@gmail.com>
Link: https://lore.kernel.org/r/05cc97a114269ee55ac9a91c61493c885fcc0193.1617962215.git.fabioaiuto83@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>