[new validation engine] remove old open-rewrite based validation code

[martinlippert]

Once the new validation engine is merged, we should go ahead and cleanup the code base, especially removing all the code and preferences that are related to the OpenRewrite based source reconciling.

(follow-up action around new validation engine, based on work done for #1068)

[BoykoAlex]

Fixed with da89df6 (at least majority of Rewrite related code is gone)