Events on personal ical feed are now excluded if someone deregistered

Simcha van Collem
2019-11-20T21:39:38+01:00

Closes #963

#### Previous behaviour
Steps to reproduce:

1. Deregister from event
2. Download personal iCal feed
3. See the event despite you deregistered

#### New behaviour
Steps to validate that it works:

1. Deregister from event...

Closes #963 (closed)

Previous behaviour

Steps to reproduce:

1. Deregister from event

2. Download personal iCal feed

3. See the event despite you deregistered

New behaviour

Steps to validate that it works:

1. Deregister from event

2. Download personal iCal feed

3. No event there