Check if sharding is enabled inside ~ScopedOperationCompletionShardingActions

If the config database gets dropped while we are setting up config.system.sessions inside
LogicalSessionCacheImpl::_refresh, we will get a CannotImplicitlyCreateCollection error. This error is then handled inside the destructor of ScopedOperationCompletionShardingActions which tries to do getConfigServer(). This will trigger a segmentation fault if the cluster is not sharded.