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/manager.h

@@ -22,7 +22,6 @@
 ***/
 
 #include <stdbool.h>
-#include <inttypes.h>
 #include <stdio.h>
 
 #include "sd-bus.h"
@@ -31,7 +30,6 @@
 #include "cgroup-util.h"
 #include "hashmap.h"
 #include "list.h"
-#include "set.h"
 #include "ratelimit.h"
 
 /* Enforce upper limit how many names we allow */
@@ -70,14 +68,11 @@ typedef enum StatusType {
         STATUS_TYPE_EMERGENCY,
 } StatusType;
 
-#include "unit.h"
 #include "job.h"
 #include "path-lookup.h"
 #include "execute.h"
 #include "unit-name.h"
-#include "exit-status.h"
 #include "show-status.h"
-#include "failure-action.h"
 
 struct Manager {
         /* Note that the set of units we know of is allowed to be