Revert "sd-bus: do not connect to dbus-1 socket when kdbus is available"

This reverts commit d4d00020d6. The idea of
the commit is broken and needs to be reworked. We really cannot reduce
the bus-addresses to a single address. We always will have systemd with
native clients and legacy clients at the same time, so we also need both
addresses at the same time.

src/core/timer.c

@@ -27,6 +27,7 @@
 #include "dbus-timer.h"
 #include "special.h"
 #include "bus-util.h"
+#include "bus-error.h"
 
 static const UnitActiveState state_translation_table[_TIMER_STATE_MAX] = {
         [TIMER_DEAD] = UNIT_INACTIVE,