Remove postgres service for Github Action

[jtwalsh0]

The postgres service in the github test suite is unnecessary: https://github.com/dssg/triage/blob/ab052a7a09a430e905823fb5cf4b47cb2ffbc361/.github/workflows/test.yaml#L9-L22

testing.postgresql initializes a local database. The service is created but goes unused.

I ran test.yaml without the service and it still passed: https://github.com/jtwalsh0/triage/actions/runs/2443440699