Host Deletion function performs no check for the type of Host

#Bug

Expected behaviour:
- Participants should not be allowed to remove the admin of the host team.
- Admin should be provided proper warning when he/she tries to remove himself/herself from the team.

Observed behaviour:
- When Admin tries to remove himself, the whole team along with his members get removed.
- The participant of the host team is able to remove it's admin.

Steps to reproduce the problem:
After writing controller function for deleting host.
Go to Host Team -> Create a new host team -> Add members to it -> Try deleting Admin

Operating System:
Ubuntu 18.04

Browser:
Google Chrome


Reference: https://github.com/Cloud-CV/EvalAI/blob/master/apps/hosts/views.py#L204-L206