Remove rake and thor/group from top-level Rakefile
Remove rake and thor/group from top-level Rakefile

We don't need to require rake from a Rakefile, if we have run the
Rakefile we can assume that has been done by rake.

We don't need thor/group anymore. It was required ages ago when sandbox
generation was a part of the top-level Rakefile.

pervino/solidus,pervino/solidus,pervino/solidus,pervino/solidus