update delete ip from pool endpoint to reflect reality

Docs for removing an ip from a pool do not work, the endpoint takes a resource as part of the URI not inside the request body.

Current docs api:
```bash
curl -X DELETE https://api.sendgrid.com/v3/ips/pools/earthbound/ips -d '{"ip": "0.0.0.0"}
>>  {"errors":[{"field":null,"message":"method not allowed"}]}
```

Correct way
```bash
curl -X DELETE https://api.sendgrid.com/v3/ips/pools/earthbound/ips/0.0.0.0
>> (No content, returns 204)
```