tree-wide: Clean up includes

This removes more unused includes from the components already cleaned
up in #37467 and #37457.

Split out of #37344.

src/firstboot/firstboot.c

@@ -2,7 +2,6 @@
 
 #include <fcntl.h>
 #include <getopt.h>
-#include <linux/loop.h>
 #include <unistd.h>
 
 #include "sd-bus.h"
@@ -51,7 +50,6 @@
 #include "terminal-util.h"
 #include "time-util.h"
 #include "tmpfile-util-label.h"
-#include "umask-util.h"
 #include "user-util.h"
 #include "vconsole-util.h"