Revert "MDEV-12445 : Rocksdb does not shutdown worker threads and aborts in memleak check on server shutdown"

This reverts commit 6f1f911. because it doesn't do anything now (the server doesn't check my_disable_leak_check) and it never did anything before (because without `extern` it simply created a local instance of my_disable_leak_check, did not affect server's my_disable_leak_check).

Author: vuvova

sql/mysqld.cc

@@ -365,7 +365,6 @@ static bool volatile select_thread_in_use, signal_thread_in_use;
 static volatile bool ready_to_exit;
 static my_bool opt_debugging= 0, opt_external_locking= 0, opt_console= 0;
 static my_bool opt_short_log_format= 0, opt_silent_startup= 0;
-bool my_disable_leak_check= false;
 
 uint kill_cached_threads;
 static uint wake_thread;

storage/rocksdb/ha_rocksdb.cc

@@ -114,7 +114,6 @@ int thd_binlog_format(const MYSQL_THD thd);
 bool thd_binlog_filter_ok(const MYSQL_THD thd);
 }
 
-MYSQL_PLUGIN_IMPORT bool my_disable_leak_check;
 extern my_bool opt_core_file;
 
 // Needed in rocksdb_init_func
@@ -5688,13 +5687,6 @@ static int rocksdb_init_func(void *const p) {
  }
 #endif
 
- /**
- Rocksdb does not always shutdown its threads, when
- plugin is shut down. Disable server's leak check
- at exit to avoid crash.
- */
- my_disable_leak_check = true;
-
  err = my_error_register(rdb_get_error_messages, HA_ERR_ROCKSDB_FIRST,
  HA_ERR_ROCKSDB_LAST);
  if (err != 0) {