Follow-up to MDEV-13407: Remove fil_wait_crypt_bg_threads()

Tables whose reference count is not zero will be crash-safely
dropped in the background when the count reaches zero. Therefore,
it is no longer necessary to wait for all references to be released
before possibly adding the table to the background queue.

storage/innobase/row/row0mysql.cc

@@ -3240,37 +3240,6 @@ row_mysql_lock_table(
 	return(err);
 }
 
-static
-void
-fil_wait_crypt_bg_threads(
-	dict_table_t* table)
-{
-	time_t start = time(0);
-	time_t last = start;
-
-	while (table->get_ref_count()> 0) {
-		dict_mutex_exit_for_mysql();
-		os_thread_sleep(20000);
-		dict_mutex_enter_for_mysql();
-		time_t now = time(0);
-
-		if (now >= last + 30) {
-			ib::warn()
-				<< "Waited " << now - start
-				<< " seconds for ref-count on table: "
-				<< table->name << " space: " << table->space;
-			last = now;
-		}
-		if (now >= start + 300) {
-			ib::warn()
-				<< "After " << now - start
-				<< " seconds, gave up waiting "
-				<< "for ref-count on table: " << table->name
-				<< " space: " << table->space;
-			break;
-		}
-	}
-}
 /** Drop ancillary FTS tables as part of dropping a table.
 @param[in,out]	table		Table cache entry
 @param[in,out]	trx		Transaction handle
@@ -3647,9 +3616,6 @@ row_drop_table_for_mysql(
 	shouldn't have to. There should never be record locks on a table
 	that is going to be dropped. */
 
-	/* Wait on background threads to stop using table */
-	fil_wait_crypt_bg_threads(table);
-
 	if (table->get_ref_count() > 0 || table->n_rec_locks > 0
 	    || lock_table_has_locks(table)) {
 		goto defer;