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/core/exec-invoke.c

@@ -1,9 +1,9 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 
 #include <grp.h>
-#include <linux/sched.h>
 #include <linux/securebits.h>
 #include <poll.h>
+#include <sched.h>
 #include <sys/eventfd.h>
 #include <sys/ioctl.h>
 #include <sys/ioprio.h>
@@ -15,7 +15,7 @@
 
 #include "sd-messages.h"
 
-#include "apparmor-util.h"
+#include "apparmor-util.h"      /* IWYU pragma: keep */
 #include "argv-util.h"
 #include "ask-password-api.h"
 #include "barrier.h"