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/core/unit-printf.c

@@ -19,16 +19,13 @@
   along with systemd; If not, see <http://www.gnu.org/licenses/>.
 ***/
 
-#include "sd-id128.h"
 #include "unit.h"
 #include "specifier.h"
-#include "path-util.h"
 #include "strv.h"
 #include "unit-name.h"
 #include "unit-printf.h"
 #include "macro.h"
 #include "cgroup-util.h"
-#include "special.h"
 
 static int specifier_prefix_and_instance(char specifier, void *data, void *userdata, char **ret) {
         Unit *u = userdata;