This script removes dangling rows from the database, for example
'trace' entries with a variant_id not mentioned in the 'variants'
table, or result rows referencing a nonexistent 'fsppilot' entry.
IOW, this script enforces referential integrity as it would be
maintained by foreign key constraints (that can only be used with
InnoDB tables).
Change-Id: I4dce1e46277d470f8c3eca31447ca71f63c6353f
