MDEV-28541 Unused counter Innodb_encryption_key_rotation_list_length

The counter srv_stats.key_rotation_list_length is never updated, and
therefore Innodb_encryption_key_rotation_list_length will always be 0.

The view INFORMATION_SCHEMA.INNODB_TABLESPACES_ENCRYPTION comes close
to reporting this information.

storage/innobase/handler/ha_innodb.cc

@@ -1209,9 +1209,6 @@ static SHOW_VAR innodb_status_variables[]= {
   {"encryption_rotation_estimated_iops",
   (char*) &export_vars.innodb_encryption_rotation_estimated_iops,
    SHOW_LONG},
-  {"encryption_key_rotation_list_length",
-  (char*)&export_vars.innodb_key_rotation_list_length,
-   SHOW_LONGLONG},
   {"encryption_n_merge_blocks_encrypted",
   (char*)&export_vars.innodb_n_merge_blocks_encrypted,
    SHOW_LONGLONG},

storage/innobase/include/srv0srv.h

@@ -181,9 +181,6 @@ struct srv_stats_t
 	/** Number of log scrub operations */
 	ulint_ctr_64_t		n_log_scrubs;
 
-	/** Number of spaces in keyrotation list */
-	ulint_ctr_64_t		key_rotation_list_length;
-
 	/** Number of temporary tablespace blocks encrypted */
 	ulint_ctr_64_t		n_temp_blocks_encrypted;
 
@@ -1064,7 +1061,6 @@ struct export_var_t{
 	ulint innodb_encryption_rotation_pages_flushed;
 	ulint innodb_encryption_rotation_estimated_iops;
 	int64_t innodb_encryption_key_requests;
-	int64_t innodb_key_rotation_list_length;
 
 	ulint innodb_scrub_page_reorganizations;
 	ulint innodb_scrub_page_splits;

storage/innobase/srv/srv0srv.cc

@@ -1619,8 +1619,6 @@ srv_export_innodb_status(void)
 		crypt_stat.estimated_iops;
 	export_vars.innodb_encryption_key_requests =
 		srv_stats.n_key_requests;
-	export_vars.innodb_key_rotation_list_length =
-		srv_stats.key_rotation_list_length;
 
 	export_vars.innodb_scrub_page_reorganizations =
 		scrub_stat.page_reorganizations;