[BUG] Remove 3rd party GitHub action for heroku deploy

[jcockhren]

Describe the bug
The current heroku.yml workflow is designed to use a 3rd party (unverified) action for deployment to Heroku. This project leverages Heroku's new Platform API and container registry.

police-data-trust/.github/workflows/heroku.yml

Line 13 in 3a42519

- uses: akhileshns/[email protected] # This is the action

Code for Boston has not been able to deploy this app successfully using this action. We have not been able to get this action to authenticate with Heroku successfully.

To Reproduce
Steps to reproduce the behavior:

1. Merge any Pull Request into main
2. Look at the Actions tab

Expected behavior
When you merge into main, the action should at least successfully authenticate with Heroku and attempt to push a container with the latest app build.

Additional context
Using this 3rd party action should not be necessary given that the Heroku CLI comes preinstalled in Ubuntu images. See supported software