SERVER-41927 Enumerate and remove Execution-related FeatureCompatibilityVersion 4.0-dependent code and tests

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• Closed

SERVER-35060 Remove WiredTiger specific upgrade/downgrade interface from kv engine layer.

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• Closed

SERVER-36547 After 4.2 check_unique_indexes.js shouldn't rely on a specific FCV version

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• Closed

SERVER-37634 Remove FCV upgrade test from setFCV_collmod_transaction_upgrade

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• Closed

SERVER-45374 Unique index that gets rebuilt as part of startup recovery/repair is using data format version as 6 or 8 and NOT 11 or 12.

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• Closed