Remove Depreciated ticket logic

[jon-nfc]

As tickets were refactored to a new model (#564) the old code must be removed.

Tasks

• Remove old ticket viewsets

• Remove old ticket serializers

• Remove old ticket models

• Remove old ticket logic

• Remove old ticket tests

• Remove old ticket comment viewsets

• Remove old ticket comment serializers

• Remove old ticket comment models

• Remove old ticket comment logic

• Remove old ticket comment tests