MDEV-16264 fixup: Remove a useless test

Let us remove a test that frequently fails with a result difference.
This test had been added in fc279d7e
to cover a bug in thd_destructor_proxy(), which was replaced with
simpler logic in 5e62b6a5 (MDEV-16264).

mysql-test/suite/innodb/r/purge_thread_shutdown.result

-connect con1, localhost, root;
-create table t1 (a int) engine=innodb;
-insert t1 values (1),(2),(3),(4);
-delete from t1 where a=1;
-select user,state from information_schema.processlist order by 2;
-user	state
-root	
-root	Filling schema table
-set global debug_dbug='+d,only_kill_system_threads';
-set global innodb_fast_shutdown=0;
-shutdown;
-connection default;
-disconnect con1;
-select user,state from information_schema.processlist order by 2;
-user	state
-root	Filling schema table
-set global innodb_fast_shutdown=1;
-select user,state from information_schema.processlist order by 2;
-user	state
-root	Filling schema table
-delete from t1 where a=3;
-set global innodb_fast_shutdown=0;
-ERROR 42000: Variable 'innodb_fast_shutdown' can't be set to the value of '0'
-kill ID;
-ERROR 70100: Connection was killed
-# restart
-drop table t1;

mysql-test/suite/innodb/t/purge_thread_shutdown.test

-source include/have_innodb.inc;
-source include/not_embedded.inc;
-source include/have_debug.inc;
-
-connect con1, localhost, root;
-create table t1 (a int) engine=innodb;
-insert t1 values (1),(2),(3),(4);
-delete from t1 where a=1;
-
-select user,state from information_schema.processlist order by 2;
-
-set global debug_dbug='+d,only_kill_system_threads';
-set global innodb_fast_shutdown=0;
-
---let $_expect_file_name= `select regexp_replace(@@tmpdir, '^.*/','')`
---let $_expect_file_name= $MYSQLTEST_VARDIR/tmp/$_expect_file_name.expect
-exec echo "wait" > $_expect_file_name;
-send shutdown;
-
-connection default;
-disconnect con1;
-
-sleep 5;
-select user,state from information_schema.processlist order by 2;
-set global innodb_fast_shutdown=1;
-
-let $wait_condition=select count(*) = 0 from information_schema.processlist where user='system user';
-source include/wait_condition.inc;
-select user,state from information_schema.processlist order by 2;
-
-delete from t1 where a=3;
-error ER_WRONG_VALUE_FOR_VAR;
-set global innodb_fast_shutdown=0;
-
-# Get id with space prefix to ensure that replace_result doesn't replace
-# the error code
-let $me=`select concat(' ', connection_id())`;
-replace_result $me ID;
-error ER_CONNECTION_KILLED;
-eval kill $me;
-
-source include/start_mysqld.inc;
-drop table t1;