4.0 | Zend.Debug.CodeAnalyzer: remove sniff

I have the impression that the Zend Code Analyzer tool as stand-alone tool is no longer available. Please correct me if I'm wrong.

I propose to remove the sniff which allowed for running that tool via PHPCS in PHPCS 4.0, along the same lines as was already done for external JS/CSS tools in commit ea52e7b.

Author: jrfnl