README: a lot of packages mentioned in the readme are not really needed, simplify
README: a lot of packages mentioned in the readme are not really needed, simplify

libssl-dev, gzip, python, gcc have never been really needed for Etherpad itself.
They were probably needed back in the day to manually compile nodejs.

cloudfoundry-community/etherpad-lite-cf,aptivate/etherpad-lite,joequant/etherpad-lite,joequant/etherpad-lite,cloudfoundry-community/etherpad-lite-cf,aptivate/etherpad-lite,cloudfoundry-community/etherpad-lite-cf,aptivate/etherpad-lite,storytouch/etherpad-lite,aptivate/etherpad-lite,ether/etherpad-lite,joequant/etherpad-lite,storytouch/etherpad-lite,ether/etherpad-lite,cloudfoundry-community/etherpad-lite-cf,joequant/etherpad-lite,storytouch/etherpad-lite,ether/etherpad-lite