tests: Remove id from db fixtures.

It seems that PostgreSQL will not update the autoincrement index of the table when inserting rows with an id set. Later inserts without an id set will then fail, because they get assigned an id that already exists.

MySQL seems to handle this just fine.

Why the id column was added in the first place, one may wonder, but that's how it were.

In any case, this broke the PostgreSQL tests in the gitlab CI environment. (While it mysteriously worked in my local ddev environment.) Anyways, the id column is not needed, and things work better without them.