clang-tidy: Fix all remaining misc-include-cleaner violations

- Remove unused includes
- Add common false positive headers to misc-include-cleaner.IgnoreHeaders
- Add IWYU pragma keep for uncommon false positive headers

src/shutdown/detach-md.c

@@ -3,7 +3,7 @@
   Copyright © 2010 ProFUSION embedded systems
 ***/
 
-#include <linux/major.h>
+#include <linux/major.h>        /* IWYU pragma: keep */
 #include <linux/raid/md_u.h>
 #include <sys/ioctl.h>
 

src/shutdown/shutdown.c

@@ -26,7 +26,6 @@
 #include "detach-swap.h"
 #include "errno-util.h"
 #include "exec-util.h"
-#include "extract-word.h"
 #include "fd-util.h"
 #include "fileio.h"
 #include "format-util.h"
@@ -44,7 +43,6 @@
 #include "signal-util.h"
 #include "string-util.h"
 #include "switch-root.h"
-#include "sysctl-util.h"
 #include "terminal-util.h"
 #include "time-util.h"
 #include "umount.h"