Remove Gemfile from demo/

[lcreid]

Remove the demo/Gemfile and demo/Gemfile.lock. This follows what you get when you generate a plugin or engine with rails plugin new. The Rails files, particularly config/boot.rb for the "dummy" app generated by rails plugin new refer to the Gemfile in the root directory of the gem.

We have our own test app in demo (for historical reasons). For most purposes, you can work in the demo directory as if it were a regular Rails application. But you must not put a Gemfile there, because it won't get used and you'll only confuse yourself.

This also means that prefixing bundle exec in the demo directoy won't work, because bundle won't find a Gemfile. (Unless you also prefix the command with BUNDLE_GEMFILE=<path to gemfile>.)

Note, however, that in the CI file .github/workflows/ruby.yml, we do use bundle exec. This is because all our gemfiles seem to want a different version of Rake than the one standard in the Ubuntu version. If we dodn't do bundle exec, we get the You have alread activated rake version ..., but your gemfile specifies rake version ... message.