How to remove a Github Environment

I made a little webpage/script too, to automate the process (I don't have Python installed, and I didn't see that someone else had already made a script), and this is online and putting your info will do the process automatically.

Stackblitz - Github Deployments deleter

Edit 18/07/2020: I copied the script from Stackblitz to a local snippet code in here too, just in case Stackblitz disappears:

// RECOMMENDED: Disconnect HEROKU from Github before doing this (though not strictly necessary, I think).
//See https://stackoverflow.com/a/61272173/6569950 for more info.

// PARAMETERS
const TOKEN = ""; // MUST BE `repo_deployments` authorized
const REPO = "your-repo"; // e.g. "monorepo"
const USER_OR_ORG = "your-name"; // e.g. "your-name"

// GLOBAL VARS
const URL = `https://api.github.com/repos/${USER_OR_ORG}/${REPO}/deployments`;
const AUTH_HEADER = `token ${TOKEN}`;

// UTILITY FUNCTIONS
const getAllDeployments = () =>
  fetch(`${URL}`, {
    headers: {
      authorization: AUTH_HEADER
    }
  }).then(val => val.json());

const makeDeploymentInactive = id =>
  fetch(`${URL}/${id}/statuses`, {
    method: "POST",
    body: JSON.stringify({
      state: "inactive"
    }),
    headers: {
      "Content-Type": "application/json",
      Accept: "application/vnd.github.ant-man-preview+json",
      authorization: AUTH_HEADER
    }
  }).then(() => id);

const deleteDeployment = id =>
  fetch(`${URL}/${id}`, {
    method: "DELETE",
    headers: {
      authorization: AUTH_HEADER
    }
  }).then(() => id);

// MAIN
getAllDeployments()
  .catch(console.error)
  .then(res => {
    console.log(`${res.length} deployments found`);
    return res;
  })
  .then(val => val.map(({
    id
  }) => id))
  .then(ids => Promise.all(ids.map(id => makeDeploymentInactive(id))))
  .then(res => {
    console.log(`${res.length} deployments marked as "inactive"`);
    return res;
  })
  .then(ids => Promise.all(ids.map(id => deleteDeployment(id))))
  .then(res => {
    console.log(`${res.length} deployments deleted`);
    return res;
  })
  .then(finalResult => {
    const appDiv = document.getElementById("app");
    appDiv.innerHTML = `
<h1>CLEANUP RESULT</h1>
<br>
Removed Deployments: ${finalResult.length}
<br>
<br>Ids:<br>
${JSON.stringify(finalResult)}
<br><br><br><br><br><br>
  <p>(Open up the console)</p>
`;
  });

h1,
h2 {
  font-family: Lato;
}

<div id="app">
  <h1>Github Deployment's Cleaner</h1>
  <p> You need to put the parameters in!</p>
</div>

There doesn't seem to be UI for it, but you can do it using the GitHub API.

You should probably disconnect GitHub and Heroku before doing this.

First, go to your GitHub account settings, then developer settings, then personal access tokens. Create a new token that has repo_deployments allowed. After it's generated, save the hexadecimal token, you'll need it for the upcoming API requests.

For these examples I'll assume that your username is $aaaa and your repo name is $bbbb and your access token is $tttt. Replace these with your actual username and repo name and access token. Or just use shell variables to store the actual values which will let you paste the code blocks directly.

First, list all the deployments on your repo:

curl https://api.github.com/repos/$aaaa/$bbbb/deployments

Each deployment has an id integer. Note it, and replace $iiii in the upcoming code blocks with that ID. Or create another shell variable for it.

Now you have to create an "inactive" status for that deployment:

curl https://api.github.com/repos/$aaaa/$bbbb/deployments/$iiii/statuses -X POST -d '{"state":"inactive"}' -H 'accept: application/vnd.github.ant-man-preview+json' -H "authorization: token $tttt"

And now you can delete the deployment forever:

curl https://api.github.com/repos/$aaaa/$bbbb/deployments/$iiii -X DELETE -H "authorization: token $tttt"

If you have multiple deployments, send the first request to see all the deployments that remain, and then you can delete those too if you want.

After you delete all the deployments, the environments button on the GitHub repo will disappear.

Information sourced from the GitHub deployments documentation and the GitHub oauth documentation. This worked for me.