Cleanup: Remove innobase_destroy_background_thd()

We do not need a non-inline wrapper for the function
destroy_background_thd().

storage/innobase/fts/fts0opt.cc

@@ -2965,7 +2965,7 @@ static void fts_optimize_callback(void *)
 	ib_wqueue_free(fts_optimize_wq);
 	fts_optimize_wq = NULL;
 
-	innobase_destroy_background_thd(fts_opt_thd);
+	destroy_background_thd(fts_opt_thd);
 	ib::info() << "FTS optimize thread exiting.";
 
 	os_event_set(fts_opt_shutdown_event);

storage/innobase/handler/ha_innodb.cc

@@ -127,7 +127,6 @@ void thd_clear_error(MYSQL_THD thd);
 TABLE *find_fk_open_table(THD *thd, const char *db, size_t db_len,
 			  const char *table, size_t table_len);
 MYSQL_THD create_background_thd();
-void destroy_background_thd(MYSQL_THD thd);
 void reset_thd(MYSQL_THD thd);
 TABLE *get_purge_table(THD *thd);
 TABLE *open_purge_table(THD *thd, const char *db, size_t dblen,
@@ -1477,16 +1476,6 @@ innobase_create_background_thd(const char* name)
 }
 
 
-/** Destroy a background purge thread THD.
-@param[in]	thd	MYSQL_THD to destroy */
-void
-innobase_destroy_background_thd(
-/*============================*/
-	MYSQL_THD thd)
-{
-	destroy_background_thd(thd);
-}
-
 /** Close opened tables, free memory, delete items for a MYSQL_THD.
 @param[in]	thd	MYSQL_THD to reset */
 void

storage/innobase/include/ha_prototypes.h

 /*****************************************************************************
 
 Copyright (c) 2006, 2016, Oracle and/or its affiliates. All Rights Reserved.
-Copyright (c) 2017, 2021, MariaDB Corporation.
+Copyright (c) 2017, 2022, MariaDB Corporation.
 
 This program is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free Software
@@ -512,10 +512,9 @@ innodb_set_buf_pool_size(ulonglong buf_pool_size);
 MYSQL_THD
 innobase_create_background_thd(const char* name);
 
-/** Destroy a background purge thread THD.
+/** Destroy a THD object associated with a background task.
 @param[in]	thd	MYSQL_THD to destroy */
-void
-innobase_destroy_background_thd(MYSQL_THD);
+void destroy_background_thd(MYSQL_THD thd);
 
 /** Close opened tables, free memory, delete items for a MYSQL_THD.
 @param[in]	thd	MYSQL_THD to reset */

storage/innobase/srv/srv0srv.cc

@@ -2003,7 +2003,7 @@ static void srv_shutdown_purge_tasks()
   std::unique_lock<std::mutex> lk(purge_thd_mutex);
   while (!purge_thds.empty())
   {
-    innobase_destroy_background_thd(purge_thds.front());
+    destroy_background_thd(purge_thds.front());
     purge_thds.pop_front();
   }
   n_purge_thds= 0;