remove unused includes

This patch removes includes that are not used. The removals were found with
include-what-you-use which checks if any of the symbols from a header is
in use.

src/fstab-generator/fstab-generator.c

@@ -33,7 +33,6 @@
 #include "mount-setup.h"
 #include "special.h"
 #include "mkdir.h"
-#include "fileio.h"
 #include "generator.h"
 #include "strv.h"
 #include "virt.h"