Remove the ability to specify arch type?

[jjshoe]

This ticket is mostly a discussion.

1. What is the case where you want to allow a user to specify an arch type?
2. Is it valid to have a package of a same name in all, and specific arch types?
3. How does a system behave when an i386 package is placed in an amd64 repository?

At the least I think adjusting https://github.com/krobertson/deb-s3/blob/master/lib/deb/s3/cli.rb#L177 to be arch = pkg.architecture || options[:arch] would be more correct, as long as it throws a warning.

Thoughts on this @krobertson?