Remove special pre-mysql 4.1 handling in query to fetch orphaned pages (which is really slow for large spaces)

The database queries to retrieve orphaned pages require the use of nested queries. As this is not supported in older versions of MySQL, an alternative was implemented that does not use the database that is very inefficient - it loads up all pages of the required space into memory and then checks each one to determine if it's an orphaned page - this is both memory and processor inefficient. It is particularly noticeable on larger spaces.

Given that the minimum supported version of MySQL is now 5.0, this special handling for MySQL is unnecessary and detrimental to the performance of our MySQL customers.

Action: Remove this handling.