Consider removing the fatal assertion for 4656001; or convert to a non-fatal user assertion.

In IndexBuildsCoordinator::_tryAbort(), it is a fatal error if we are unable to look up the OperationContext of an index build to interrupt using the ReplIndexBuildState::opId (set at index build startup). This fatal assertion was originally introduced in SERVER-46560. Until SERVER-47605, we would occasionally hit this fatal assertion during testing.

This assertion does not really suggest a crash-worthy scenario because if the OperationContext for an index build cannot be found, it would mean that the index build has completed (committed or aborted) and there would not be any OperationContext to interrupt for the user-initiated abort request.