Fix false config_cache_write events

On pool import when the old cache file is removed
the ereport.fs.zfs.config_cache_write event is generated.
Because zpool export always removes cache file it happens
every export - import sequence.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: loli10K <ezomori.nozomu@gmail.com>
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Signed-off-by: Arkadiusz Bubała <arkadiusz.bubala@open-e.com>
Closes openzfs#6617

module/zfs/spa_config.c

@@ -181,10 +181,12 @@ spa_config_write(spa_config_dirent_t *dp, nvlist_t *nvl)
 	 * If the nvlist is empty (NULL), then remove the old cachefile.
 	 */
 	if (nvl == NULL) {
-		err = spa_config_remove(dp);
+		err = vn_remove(dp->scd_path, UIO_SYSSPACE, RMFILE);
+		/*
+		 * Don't report an error when the cache file is already removed
+		 */
 		if (err == ENOENT)
 			err = 0;
-
 		return (err);
 	}