Well I also flubbed this answer because I responded as if you had the desktop version of PD rather than the PD Mobile app. Sorry about that!
I have the Android mobile version and don't see any way to delete an entire track. Unlike the desktop version, you can't select multiple clips at once so you'll have to click on each clip and delete them one at a time.
Maybe other users will have a better answer, but in the meantime you may want to let Cyberlink know that you'd like to be able to delete an entire track in a future version.
In the Android version, there's a tool under settings called FAQ & Send Feedback and I imagine there's a similar option in your version. I'm told the developers don't typically read forum posts, so using the in-app feedback tool will get the info to the right people.