DBusLoop: remove a layer of pointless abstraction around timeouts

DBusLoop: remove a layer of pointless abstraction around timeouts

Instead of supplying 8 tiny wrapper functions around dbus_timeout_handle,
each with a user_data parameter that's a potentially unsafe borrowed
pointer but isn't actually used, we can call dbus_timeout_handle directly
and save a lot of trouble.

One of the wrappers previously called dbus_timeout_handle repeatedly
if it returned FALSE to indicate OOM, but that timeout's handler never
actually returned FALSE, so there was no practical effect. The rest just
ignore the return, which is documented as OK to do.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=33342
Reviewed-by: Thiago Macieira <thiago@kde.org>