gluonc-core: 200-wireless: remove unneeded nil checks for uci:set_list()

uci:set_list() will delete the list when nil is passed, so there is no need
to differentiate between the cases.

package/gluon-core/luasrc/lib/gluon/upgrade/200-wireless

@@ -151,17 +151,8 @@ local function configure_radio(radio, index, config)
 	uci:set('wireless', radio, 'htmode', 'HT20')
 	uci:set('wireless', radio, 'country', site.regdom)
 
-	if config.supported_rates then
-		uci:set_list('wireless', radio, 'supported_rates', config.supported_rates)
-	else
-		uci:delete('wireless', radio, 'supported_rates')
-	end
-
-	if config.basic_rate then
-		uci:set_list('wireless', radio, 'basic_rate', config.basic_rate)
-	else
-		uci:delete('wireless', radio, 'basic_rate')
-	end
+	uci:set_list('wireless', radio, 'supported_rates', config.supported_rates)
+	uci:set_list('wireless', radio, 'basic_rate', config.basic_rate)
 
 
 	local ibss_disabled = is_disabled('ibss_' .. radio)