tree-wide: Clean up includes

This commit cleans up the includes for all the small tools across
the tree.

A few cases of returning EXIT_SUCCESS are replaced with returning
0 to avoid including <stdlib.h>.

Split out of #37344.

src/debug-generator/debug-generator.c

@@ -8,8 +8,8 @@
 #include "dropin.h"
 #include "errno-util.h"
 #include "extract-word.h"
-#include "fd-util.h"
 #include "fileio.h"
+#include "log.h"
 #include "generator.h"
 #include "initrd-util.h"
 #include "parse-util.h"