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 <jack@suse.cz>
Acked-by: Muchun Song <muchun.song@linux.dev>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Joel Granados <joel.granados@kernel.org>

kernel/printk/internal.h

@@ -4,9 +4,9 @@
  */
 #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

@@ -3,7 +3,6 @@
  * sysctl.c: General linux system control interface
  */
 
-#include <linux/sysctl.h>
 #include <linux/printk.h>
 #include <linux/capability.h>
 #include <linux/ratelimit.h>