TODO Deallocate prepared statements

[jim-parry]

Database/SQLite3/PreparedQuery::_execute(..) has todo note... finalize()

[lonnieezell]

Looks like a common method needs implemented for all of our db libs to destroy the prepared query when we're done with it. SqLite has finalize, MySQL has deallocate and Postgres doesn't appear to have anything.

[puschie286]

Postgres has deallocate too

[kenjis]

Closed by #6665