sysctl: Remove unused ctl_table forward declarations

Remove superfluous forward declarations of ctl_table from header files
where they are no longer needed. These declarations were left behind
after sysctl code refactoring and cleanup.

Reviewed-by: Jan Kara <[e-mail]>
Acked-by: Muchun Song <[e-mail]>
Reviewed-by: Petr Mladek <[e-mail]>
Acked-by: Paolo Abeni <[e-mail]>
Signed-off-by: Joel Granados <[e-mail]>

include/linux/fs.h

···
 ssize_t simple_attr_write_signed(struct file *file, const char __user *buf,
 				 size_t len, loff_t *ppos);
 
-struct ctl_table;
 int __init list_bdev_fs_names(char *buf, size_t size);
 
 #define __FMODE_EXEC		((__force int) FMODE_EXEC)

include/linux/hugetlb.h

···
 #include <linux/userfaultfd_k.h>
 #include <linux/nodemask.h>
 
-struct ctl_table;
-struct user_struct;
 struct mmu_gather;
 struct node;
 

include/linux/printk.h

···
 /* strlen("ratelimit") + 1 */
 #define DEVKMSG_STR_MAX_SIZE 10
 extern char devkmsg_log_str[DEVKMSG_STR_MAX_SIZE];
-struct ctl_table;
 
 extern int suppress_printk;
 

include/net/ax25.h

···
 	unsigned short		slave_timeout;		/* when? */
 } ax25_dama_info;
 
-struct ctl_table;
-
 typedef struct ax25_dev {
 	struct list_head	list;
 

kernel/printk/internal.h

···
  */
 #include <linux/console.h>
 #include <linux/types.h>
+#include <linux/sysctl.h>
 
 #if defined(CONFIG_PRINTK) && defined(CONFIG_SYSCTL)
-struct ctl_table;
 void __init printk_sysctl_init(void);
 int devkmsg_sysctl_set_loglvl(const struct ctl_table *table, int write,
 			      void *buffer, size_t *lenp, loff_t *ppos);

kernel/printk/sysctl.c

···
  * sysctl.c: General linux system control interface
  */
 
-#include <linux/sysctl.h>
 #include <linux/printk.h>
 #include <linux/capability.h>
 #include <linux/ratelimit.h>