* Disassociate subnets from route tables before deletion
If a route table still has subnets associated with it, it will fail
to delete:
```
"msg": "The routeTable 'rtb-abcd1234' has dependencies and cannot be deleted."
```
Avoid this by disassociating subnets before route table deletion
* Fix ec2_vpc_route_table flake8 complaints
da1c13705d