Removing JZlib from Jenkins core

[Basil Crow]

JZlib is no longer maintained, and continuing to carry a custom fork
is a burden. I have found the Java 7+ GZIPInputStream and
GZIPOutputStream classes to work well as a drop-in replacement. Once
plugins migrate to these standard Java Platform classes, we can remove
JZlib from the WAR.

Others have correctly identified the opportunity to refactor the stack
to move compression from the web framework layer (Stapler) to the
servlet container layer (Winstone/Jetty) in
https://github.com/jenkinsci/stapler/issues/130 and
https://github.com/jenkinsci/stapler/issues/265. That long-term goal
carries significantly higher implementation effort and risk, since it
is a change to interfaces and not just implementations.

[Basil Crow]

I have filed https://issues.jenkins.io/browse/JENKINS-73354 to track this task.