equalizer: Don't cleanup u->sink in sink_input_kill_cb yet
Previously, sink_input_kill_cb would cleanup u->sink an then unload the
module. However, during module unload, both save_state and dbus_done
tried to use u->sink, causing a segfault or assertion failure.
The segfault is easy to reproduce: Load module-equalizer-sink and then
press ctrl-C to terminate pulseaudio.
This commit removes the u->sink cleanup in sink_input_kill_cb, since
u->sink will be cleaned up by the module's pa__done as well (after it
has been used).