iwlwifi: scan: remove support for fw scan api v13

The fw already supports scan api v14 and the firmware version that
supports only v13 was not published, so we can remove support for v13 in
the driver.

Signed-off-by: Tova Mussai <tova.mussai@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20200417131727.11883315579a.I4f59100e457c1079c5e4c90e4930d1fa62b7ddd7@changeid