Remove unneeded "extern inline" function declarations

All of these externs are already #included as static inline
functions via corresponding headers.

Reviewed-by: Igor Kozhukhov <igor@dilos.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tomohiro Kusumi <kusumi.tomohiro@gmail.com>
Closes #13073

module/zfs/zap_leaf.c

@@ -52,8 +52,6 @@ static uint16_t *zap_leaf_rehash_entry(zap_leaf_t *l, uint16_t entry);
 
 #define	LEAF_HASH_ENTPTR(l, h)	(&zap_leaf_phys(l)->l_hash[LEAF_HASH(l, h)])
 
-extern inline zap_leaf_phys_t *zap_leaf_phys(zap_leaf_t *l);
-
 static void
 zap_memset(void *a, int c, size_t n)
 {