Revert exprengine changes to fix CI on appveyor#3668

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pfultz2 wants to merge 2 commits intodanmar:mainfrom

pfultz2:ci-expr-engine-fix

Commits on Jan 3, 2022

Revert "exprengine; add CONTRACT #define so contract-handling can be enabled/disabled"
pfultz2
committed
Revert "exprengine: better checking for uninit variables"
pfultz2
committed