This removes a lot of setup code we used to need in order to get Boulder to run,
and should reduce brittleness of tests based on Boulder changes.
This also unblocks Boulder from upgrading to MariaDB 10.1 in integration tests,
since changing to 10.1 syntax for user creation would break the current certbot
integration tests (which run 10.0).
Remove the old bootstrap scripts, which have been subsumed into letsencrypt-auto-source/pieces/bootstrappers. They no longer need to be dispatched among manually: everyone can just run letsencrypt-auto --os-packages-only, regardless of OS.
Make the root-level le-auto a symlink to the canonical version. It should thus still work for people running le-auto from a git checkout.
