Update rad length scans to use new external parallel geometry
Now that external parallel geometry is available at configuration time (!750 (merged), !757 (merged)) the rad length scan and interaction length scan scripts for Run 2 and Run 3 updated in !635 (merged) should be modify to use this and the MR in DDDB closed (lhcb-conddb/DDDB!66, lhcb-conddb/DDDB!67)