Refactor DataObject::delete() - move the logic into DataQuery

[sabina-talipova]

Description

To improve:

• move the details of the delete code in the DataQuery system
• update the code to just delete the row from the base table, and rely on cascading deletes in the DB to do the rest
• obviously, that means getting requireTable() to configure cascading deletes. This could be considered a breaking change, for some extreme edge cases

See:

silverstripe-framework/src/ORM/DataObject.php

Lines 1755 to 1758 in cf78a9d

	// TODO: This is quite ugly. To improve:
	// - move the details of the delete code in the DataQuery system
	// - update the code to just delete the base table, and rely on cascading deletes in the DB to do the rest
	// obviously, that means getting requireTable() to configure cascading deletes ;-)