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/shared/socket-label.c

@@ -19,24 +19,16 @@
   along with systemd; If not, see <http://www.gnu.org/licenses/>.
 ***/
 
-#include <assert.h>
 #include <string.h>
 #include <unistd.h>
 #include <errno.h>
-#include <stdlib.h>
-#include <arpa/inet.h>
-#include <stdio.h>
-#include <net/if.h>
-#include <sys/types.h>
 #include <sys/stat.h>
 #include <stddef.h>
-#include <sys/ioctl.h>
 
 #include "macro.h"
 #include "util.h"
 #include "mkdir.h"
 #include "missing.h"
-#include "label.h"
 #include "selinux-util.h"
 #include "socket-util.h"