Deprecate utils/redis-copy.rb in favor of redis-copy gem

When needing to do a semi-live redis copy recently from db1 on one box to db3 on another, I stumbled across the `utils/redis-copy.rb` script and ended up working it into a well-tested [gem](https://github.com/yaauie/redis-copy) that was able to handle all of the datatypes and different db numbers.

The gem has since evolved to support `DUMP/RESTORE` (iff supported by both source and destination redis processes), optional verification, and even will support `SCAN` for key-emitting in the near future. As such, I think it is a good time to deprecate the `utils/redis-copy.rb`.