Lua: Remove unneeded call in wslua_cleanup

Change-Id: I0cda00001b40e5951d680d72dbc8043cbe8b9309
Reviewed-on: https://code.wireshark.org/review/9980
Reviewed-by: Stig Bjørlykke <stig@bjorlykke.org>

epan/wslua/init_wslua.c

@@ -997,7 +997,6 @@ void wslua_cleanup(void) {
         wslua_deregister_filehandlers(L);
         wslua_deregister_menus();
         wslua_clear_plugin_list();
-        proto_free_deregistered_fields();
 
         lua_close(L);
         L = NULL;