osc.lua: observe track-list/playlist property with type nil

This partially undos the changes in de08494
for performance reasons. As mentioned in the original commit message,
these don't matter much since they change multiple times on each new
file anyway and the change was only done for correctness sake.

Fixes: #15264

player/lua/osc.lua

@@ -2561,8 +2561,8 @@ end
 
 mp.register_event("shutdown", shutdown)
 mp.register_event("start-file", request_init)
-mp.observe_property("track-list", "native", request_init)
-mp.observe_property("playlist", "native", request_init)
+mp.observe_property("track-list", nil, request_init)
+mp.observe_property("playlist", nil, request_init)
 mp.observe_property("chapter-list", "native", function(_, list)
     list = list or {}  -- safety, shouldn't return nil
     table.sort(list, function(a, b) return a.time < b.time end)