Remove gemcache

PT 41851145

This removes the gemcache from framework.  Developers should now use [Bundler](http://gembundler.com/) (which hopefully they are already using).

For new users, this means the following minimal steps will be needed to get started with Metasploit:

    git clone git://github.com/rapid7/metasploit-framework.git
    gem install bundler
    bundle install