Update fields for Event Tasks

[maneesha]

Right now, for Event Tasks we have four fields - Person, Role, Title, URL.
We have never used the Title or URL field so these should be removed at least from the UI.
I will leave it to @pbanaszkiewicz to decide if there is a reason to keep them in the back end database model.

[maneesha]

@pbanaszkiewicz I can start working on this PR if you let me know - should we change just the UI, or should we remove these fields from the model as well?

[pbanaszkiewicz]

@maneesha I don't think title or URL are used. I think you can remove them from both UI and database.

Once you remove the fields and apply the migration, you should run the tests to figure out if something broke.

Finally the database documentation should be updated to reflect removal of these fields.