Remove final K&R definitions

Clang trunk now warns -Wstrict-prototypes on this, and they're removed
in C2x

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes openzfs#13447

cmd/zed/agents/zfs_mod.c

@@ -1073,7 +1073,7 @@ zfs_enum_pools(void *arg)
  * For now, each agent has its own libzfs instance
  */
 int
-zfs_slm_init()
+zfs_slm_init(void)
 {
 	if ((g_zfshdl = libzfs_init()) == NULL)
 		return (-1);
@@ -1099,7 +1099,7 @@ zfs_slm_init()
 }
 
 void
-zfs_slm_fini()
+zfs_slm_fini(void)
 {
 	unavailpool_t *pool;
 	pendingdev_t *device;

cmd/zed/zed_disk_event.c

@@ -362,7 +362,7 @@ zed_udev_monitor(void *arg)
 }
 
 int
-zed_disk_event_init()
+zed_disk_event_init(void)
 {
 	int fd, fflags;
 
@@ -398,7 +398,7 @@ zed_disk_event_init()
 }
 
 void
-zed_disk_event_fini()
+zed_disk_event_fini(void)
 {
 	/* cancel monitor thread at recvmsg() */
 	(void) pthread_cancel(g_mon_tid);
@@ -416,13 +416,13 @@ zed_disk_event_fini()
 #include "zed_disk_event.h"
 
 int
-zed_disk_event_init()
+zed_disk_event_init(void)
 {
 	return (0);
 }
 
 void
-zed_disk_event_fini()
+zed_disk_event_fini(void)
 {
 }