drop unused fuzzystrmatch postgres extension

[syphar]

we don't use that since we migrated to using the crates.io search api a couple of years ago.

This also means we don't need the custom Dockerfile-postgres.

I adapted the initial migration, and made the reverse migration a noop,
because otherwise our testing would fail creating the extension in the new docker postgres image, since we don't create that with install_extensions.sql any more.

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[syphar]

r? @GuillaumeGomez

[GuillaumeGomez]

Nice!