tree-wide: drop redundant inclusion of linux/prctl.h

sys/prctl.h anyway includes linux/prctl.h and actually these .c files
includes sys/prctl.h. Hence, it is not necessary to explicitly include
linux/prctl.h.

src/basic/capability-util.c

@@ -1,6 +1,5 @@
 /* SPDX-License-Identifier: LGPL-2.1-or-later */
 
-#include <linux/prctl.h>
 #include <stdatomic.h>
 #include <stdio.h>
 #include <sys/prctl.h>