conf-parser: Reduce transitive includes

src/oom/oomd-manager-bus.c

@@ -2,6 +2,7 @@
 
 #include <linux/capability.h>
 
+#include "alloc-util.h"
 #include "bus-common-errors.h"
 #include "bus-polkit.h"
 #include "fd-util.h"

src/oom/oomd-manager.c

@@ -3,6 +3,7 @@
 #include "sd-daemon.h"
 #include "sd-json.h"
 
+#include "alloc-util.h"
 #include "bus-log-control-api.h"
 #include "bus-polkit.h"
 #include "bus-util.h"