Remove unused SRV_MASTER_PURGE_INTERVAL

The symbol SRV_MASTER_PURGE_INTERVAL became unused in
mysql/mysql-server@42f36919584e82c621dbec1e69fd05ab023c54c6
when separate purge threads were introduced in MySQL 5.6.5.

storage/innobase/srv/srv0srv.cc

@@ -3,7 +3,7 @@
 Copyright (c) 1995, 2017, Oracle and/or its affiliates. All Rights Reserved.
 Copyright (c) 2008, 2009 Google Inc.
 Copyright (c) 2009, Percona Inc.
-Copyright (c) 2013, 2019, MariaDB Corporation.
+Copyright (c) 2013, 2020, MariaDB Corporation.
 
 Portions of this file contain modifications contributed and copyrighted by
 Google, Inc. Those modifications are gratefully acknowledged and are described
@@ -527,7 +527,6 @@ current_time % 60 == 0 and no tasks will be performed when
 current_time % 5 != 0. */
 
 # define	SRV_MASTER_CHECKPOINT_INTERVAL		(7)
-# define	SRV_MASTER_PURGE_INTERVAL		(10)
 #ifdef MEM_PERIODIC_CHECK
 # define	SRV_MASTER_MEM_VALIDATE_INTERVAL	(13)
 #endif /* MEM_PERIODIC_CHECK */

storage/xtradb/srv/srv0srv.cc

@@ -3,7 +3,7 @@
 Copyright (c) 1995, 2017, Oracle and/or its affiliates. All Rights Reserved.
 Copyright (c) 2008, 2009 Google Inc.
 Copyright (c) 2009, Percona Inc.
-Copyright (c) 2013, 2019, MariaDB Corporation.
+Copyright (c) 2013, 2020, MariaDB Corporation.
 
 Portions of this file contain modifications contributed and copyrighted by
 Google, Inc. Those modifications are gratefully acknowledged and are described
@@ -678,7 +678,6 @@ current_time % 60 == 0 and no tasks will be performed when
 current_time % 5 != 0. */
 
 # define	SRV_MASTER_CHECKPOINT_INTERVAL		(7)
-# define	SRV_MASTER_PURGE_INTERVAL		(10)
 #ifdef MEM_PERIODIC_CHECK
 # define	SRV_MASTER_MEM_VALIDATE_INTERVAL	(13)
 #endif /* MEM_PERIODIC_CHECK */