Event Requests set to Venue TBD do not clear Venue fields

**Describe the bug**
The Venue TBD checkbox does not clear out venue information causing an incorrect venue to be associated with an event. Furthermore, the events do not show in the TBD event report because the venue is not blank.

I noticed this when cloning a prior request and then selecting TBD. The cloned record's venue was still associated with the second event even though the fields were hidden. The form appears to hide the fields, but save whatever is in the fields.

**Expected behavior**
I would expect the venue information to be reset if TBD is selected. This would prevent confusion on ftc-events, and allow the event to show up on the Venue TBD report in ftc-scoring.

Trace the Venue TBD checkbox in the event-request form and the save path for cloned requests; inspect how ftc-events and ftc-scoring consume venue fields. Done means selecting TBD removes the venue data on save and the event appears in the Venue TBD report.

Written by the indexing model from the issue text.