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.c

@@ -80,8 +80,6 @@ static int zap_iterate_prefetch = B_TRUE;
 
 int fzap_default_block_shift = 14; /* 16k blocksize */
 
-extern inline zap_phys_t *zap_f_phys(zap_t *zap);
-
 static uint64_t zap_allocate_blocks(zap_t *zap, int nblocks);
 
 void