osc: make cycling visibility an input.conf key binding

As builtin script, it should not register global key bindings, and add
them to input.conf instead. This is similar to what stats.lua does.

etc/input.conf

@@ -142,6 +142,7 @@
 #l ab-loop                              # Set/clear A-B loop points
 #L cycle-values loop-file "inf" "no"    # toggle infinite looping
 #ctrl+c quit 4
+#DEL script-binding osc/visibility      # cycle OSC display
 
 # Apple Remote section
 #AR_PLAY cycle pause

player/lua/osc.lua

@@ -2387,6 +2387,6 @@ end
 
 visibility_mode(user_opts.visibility, true)
 mp.register_script_message("osc-visibility", visibility_mode)
-mp.add_key_binding("del", function() visibility_mode("cycle") end)
+mp.add_key_binding(nil, "visibility", function() visibility_mode("cycle") end)
 
 set_virt_mouse_area(0, 0, 0, 0, "input")