gs-lock-plug: remove function casting

[rbuj]

dialog_timed_out and response_cancel_idle_cb are GSourceFunc functions which are not called outside g_timeout_add; for that reason, they don't need a function casting like date_time_update, which is called within g_timeout_add and directly date_time_update (plug);

[raveit65]

Why not calling reviewers?

[monsta]

Interesting, with the correct function return type (gboolean) the casting via (GSourceFunc) doesn't cause a warning. That's casting of a pointer to some type to a pointer to void (in the function argument), same as done with response_cancel_idle_cb and dialog_timed_out in the same file.

[rbuj]

@monsta done