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_micro.c

@@ -41,8 +41,6 @@
 #include <sys/sunddi.h>
 #endif
 
-extern inline mzap_phys_t *zap_m_phys(zap_t *zap);
-
 static int mzap_upgrade(zap_t **zapp,
     void *tag, dmu_tx_t *tx, zap_flags_t flags);