btrfs: cleanup kobject.h includes

The kobject should be pulled in via sysfs.h and that needs to include it
because it needs various definitions like kobj_attribute or kobject.
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -16,7 +16,6 @@
 #include <linux/backing-dev.h>
 #include <linux/wait.h>
 #include <linux/slab.h>
-#include <linux/kobject.h>
 #include <trace/events/btrfs.h>
 #include <asm/kmap_types.h>
 #include <asm/unaligned.h>

fs/btrfs/sysfs.c

@@ -8,7 +8,6 @@
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 #include <linux/completion.h>
-#include <linux/kobject.h>
 #include <linux/bug.h>
 
 #include "ctree.h"

fs/btrfs/sysfs.h

@@ -3,6 +3,8 @@
 #ifndef BTRFS_SYSFS_H
 #define BTRFS_SYSFS_H
 
+#include <linux/kobject.h>
+
 enum btrfs_feature_set {
 	FEAT_COMPAT,
 	FEAT_COMPAT_RO,