remove unused zlib dependency

[jelhan]

The zlib dependency is not needed anymore. It was refactored out of the code long time ago. But missed to be removed from the list of dependencies.

At the same time it caused the installation of the NPM package to fail in consuming apps in some cases:

npm error code 127
npm error path /home/main/Code/open-source/croodle/node_modules/zlib
npm error command failed
npm error command sh -c node-waf clean || true; node-waf configure build
npm error sh: 1: node-waf: not found

This is a result of the package being very old. It was released in 2011. The build infrastructure it relies on was deprecated long ago.