Groovy postbuild should not mandatory depend on workflow

Installing groovy-postbuild-2.3 causes installing many dependent plugins:

• Script Security Plugin
• Pipeline: Step API
• MapDB API Plugin
• SCM API Plugin
• Subversion Plug-in
• Pipeline: SCM Step
• Pipeline: API
• Durable Task Plugin
• Pipeline: Execution Support
• JavaScript GUI Lib: jQuery bundles (jQuery and jQuery UI) plugin
• JavaScript GUI Lib: ACE Editor bundle plugin
• Pipeline: Groovy CPS Execution

This is mainly caused for groovy-potbuild-2.3 starts to depend on workflow-cps to support workflow (JENKINS-26918).
This is not a mandatory feature, and those dependencies should be optional.

Note: Script Security plugin is mandatory for its security model.