Remove defunct script/rails file

This was originally added in 2012 in this original commit [1] with
Rails v3.2.3.

However, `bin/rails` was added in 2015 in this commit [2] as part
of #352 which upgraded the app to Rails v4. And this is now the
canonical location [3] for the `rails` script in our current version of
Rails (v7.0.8).

It's confusing and potentially problematic to have both scripts in the
repo, so I've removed the older one.

[1]: d82798a
[2]: 640ae2f
[3]: https://github.com/rails/rails/tree/v7.0.8/railties/lib/rails/generators/rails/app/templates/bin