FreeBSD: remove support for FreeBSD < 13.0-RELEASE (#16372)

This includes the last 12.x release (now EOL) and 13.0 development
versions (<1300139).

Sponsored-by: https://despairlabs.com/sponsor/

Signed-off-by: Rob Norris <robn@despairlabs.com>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>

include/os/freebsd/spl/sys/random.h

@@ -30,9 +30,7 @@
 #define	_OPENSOLARIS_SYS_RANDOM_H_
 
 #include_next <sys/random.h>
-#if  __FreeBSD_version >= 1300108
 #include <sys/prng.h>
-#endif
 
 static inline int
 random_get_bytes(uint8_t *p, size_t s)
@@ -51,7 +49,7 @@ random_get_pseudo_bytes(uint8_t *p, size_t s)
 static inline uint32_t
 random_in_range(uint32_t range)
 {
-#if defined(_KERNEL) && __FreeBSD_version >= 1300108
+#if defined(_KERNEL)
 	return (prng32_bounded(range));
 #else
 	uint32_t r;