shared: Clean up includes

Split out of #37344.

src/shared/killall.c

@@ -3,26 +3,22 @@
   Copyright © 2010 ProFUSION embedded systems
 ***/
 
-#include <errno.h>
 #include <signal.h>
 #include <sys/wait.h>
-#include <unistd.h>
 
 #include "alloc-util.h"
-#include "constants.h"
-#include "dirent-util.h"
 #include "errno-util.h"
 #include "fd-util.h"
 #include "format-util.h"
 #include "initrd-util.h"
 #include "killall.h"
 #include "log.h"
-#include "parse-util.h"
+#include "pidref.h"
 #include "process-util.h"
 #include "set.h"
-#include "stdio-util.h"
 #include "string-util.h"
 #include "terminal-util.h"
+#include "time-util.h"
 
 static int argv_has_at(const PidRef *pid) {
         int r;