Remove BindVisitor dependency given it's deprecated in Arel 9.0

[pwen]

Rails 5.2 requires Arel 9.0, which is what we're at; whereas the gem depends on Arel 8.0.
arel/visitors/visitor was removed in Arel 9.0; note that this was required for MySQL adapter only, and we don't need that. Patching this so it can be compatible with our use case.

This PR is probably not going to be merged; the plan is that cnce the original gem has fixed this, we can pull the original gem instead. Some PR pending in that repo: localytics#26

CI failed, seems unrelated 🤔

sql: could not connect to server: No such file or directory
	Is the server running locally and accepting
	connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?
The command "bin/ci-setup" failed and exited with 2 during .

I ran the changes locally and it seems to work with core.

[jobertabma]

Perhaps update this comment, too.