* contracts-bedrock, ci: remove slither

Remove the committed in `slither-report.json` since it is not being used
as part of code review. Also remove running it as part of CI. We can
choose to add it back when we have the time for somebody to own making
it a first class tool, but since we haven't triaged the database yet
it only adds noise to PRs by adding extra diff and extra overhead by
forcing a regeneration of the report.

It hasn't found any issues in our code and our other checks are much
better at finding issues in the code.

Leaving the slither commands in the `package.json` for now but if we
do not commit to using slither in a way that is very helpful for us
in 6 months or so, then we should just remove the commands as well.

Maybe we can adopt a way of using slither where it is used before
doing releases of contracts or before going to audit. Having the diff
as part of code review is not super helpful for code reviewers.
It just adds noise in the current form.

* Kick build

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Co-authored-by: Matthew Slipper <me@matthewslipper.com>