In 4.2 release unique indexes got an upgrade and their internal wiredtiger specific version changed accordingly. check_unique_indexes.js currently checks for the unique indexes to have the correct versions but relies on obtaining current FCV and comparing it to statically coded "4.2" in the script.

Once we are past 4.2, we can just assert that we have the correct versions, there wont be a need to check for the FCV. This ticket is filed to update check_unique_indexes.js after 4.2 to do the same.