The only solution is to select and delete the cross dissolves either individually or by holding down command and click on each one. You can then drag each clip that is still in a secondary storyline out of the black groupings but you run the risk of loosing sync. I just did some testing and it seems better to start from the end of your clip and make your way to the beginning. If you take the first clip out of a group, the following clips in the group snap to the beginning of the group. Whereas if you start at the end everything stays in place easier. If its a big project, I personally would just delete the dissolves and leave the groups alone if they are already in the correct places.