[Core] Refactor RectifiedAnalyzer to only exclude Class_

[samsonasik]

This is next step for verify node re-changed by rule for :

Same Rector Rule <-> Same Node <-> Same File

which previously, we excluded the following nodes as limitation of Nodes to be checked:

• Assign
• Class_.

This PR remove Assign from exclusion, by change AssignRemover to look up parent node, if parent node is an Assign, recursive call the AssignRemover to the parent node.

With its change, the ExprUsedInNextNodeAnalyzer no longer need a tweak for check next node is an If_ and modified by RemoveAlwaysElseRector, as already handled in RectifiedAnalyzer for Assign check.

[samsonasik]

All checks have passed 🎉 @TomasVotruba it is ready for review.

[TomasVotruba]

Thank you 👍