Remove outdated known issue.

Author: bgrainger

docs/content/overview/known-issues.md

@@ -12,5 +12,4 @@ Known Issues
 ============
 
 * Prepared statements are not supported: [#397](https://github.com/mysql-net/MySqlConnector/issues/397).
-* MySQL spatial data types are not supported: [#70](https://github.com/mysql-net/MySqlConnector/issues/70).
 * Some `MySql.Data` connection string settings are not supported by this library. See [Connection Options](connection-options/) for a list of supported options.