tree-wide: drop sched.h when missing_sched.h is included

src/nspawn/nspawn.c

@@ -9,7 +9,6 @@
 #include <linux/fs.h>
 #include <linux/loop.h>
 #include <pwd.h>
-#include <sched.h>
 #if HAVE_SELINUX
 #include <selinux/selinux.h>
 #endif

src/test/test-process-util.c

@@ -1,7 +1,6 @@
 /* SPDX-License-Identifier: LGPL-2.1+ */
 
 #include <fcntl.h>
-#include <sched.h>
 #include <sys/mount.h>
 #include <sys/personality.h>
 #include <sys/prctl.h>

src/test/test-seccomp.c

@@ -2,7 +2,6 @@
 
 #include <fcntl.h>
 #include <poll.h>
-#include <sched.h>
 #include <stdlib.h>
 #include <sys/eventfd.h>
 #include <sys/mman.h>