cycle-deinterlace-pullup.lua: fix unused variable warnings

TOOLS/lua/cycle-deinterlace-pullup.lua

@@ -19,7 +19,7 @@ script_name = mp.get_script_name()
 pullup_label = string.format("%s-pullup", script_name)
 
 function pullup_on()
-    for i,vf in pairs(mp.get_property_native('vf')) do
+    for _, vf in pairs(mp.get_property_native('vf')) do
         if vf['label'] == pullup_label then
             return "yes"
         end