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/sysctl/sysctl.c

@@ -10,8 +10,6 @@
 #include "constants.h"
 #include "creds-util.h"
 #include "errno-util.h"
-#include "fd-util.h"
-#include "fileio.h"
 #include "glob-util.h"
 #include "hashmap.h"
 #include "log.h"