Removed the is installed check

Hello,

I really like your webpi chef recipe-- thanks for creating this!

I recently removed the installed check because WebPI actually handles this scenario gracefully and does nothing if everything is installed.  Additionally, it adds any missing dependencies if it finds them.  I was having a lot of problems getting this script to work because while I had a specific application already installed that I was requesting, it did not have one of the dependencies.  After removing these checks everything worked like a charm and I was able to re-run again after it had already been installed.

Please let me know if you find this acceptable.

Thanks again,
Josh