Remove most of DMLFunctions

Including (old) Cursor, Scan, RowCollector, TableStatistics, IndexCursorUnidirectionalLexicographic and all associated helpers.

The only interesting + is rewrite of DMLFunctions#truncateTable() using GroupScan -> Filter -> Delete instead of the old scanSome.

For those counting at home: Yes, that really is ~9K lines of unused code being removed.