GistAPI

function UserInfo(name, token) {
  this.name = name;
  this.token = token;
}

function Gists(userInfo) {
  let commonOptions = {
    accept: "application/vnd.github.v3+json",
    muteHttpExceptions: true,
    headers: {
      "Authorization": `Basic ${Utilities.base64Encode(`${userInfo.name}:${userInfo.token}`)}`
    },
  };

  let GistFileInfo = function(jsonGistFile) {
    this.name = jsonGistFile.filename;
    this.size = jsonGistFile.size;
  }

  let GistInfo = function(jsonGist) {
    this.id = jsonGist.id;
    this.description = jsonGist.description;
    this.url = jsonGist.url;
    this.isPublic = jsonGist.public;
    this.files = Object.getOwnPropertyNames(jsonGist.files).map(fileNode => new GistFileInfo(jsonGist.files[fileNode]));
  }

  let getError = function(response) {
    return JSON.parse(response.getContentText()).message;
  }

  this.list = function(isPublic) {
    result = [];

    let response = UrlFetchApp.fetch(`https://api.github.com/gists`, commonOptions);

    if (response.getResponseCode() !== 200)
      throw new Error(getError(response));

    let allGists = JSON.parse(response.getContentText());
    for (i in allGists)
      if (allGists[i].public === isPublic)
        result.push(new GistInfo(allGists[i]));

    return result;
  }

  this.getGist = function(id) {
    let response = UrlFetchApp.fetch(`https://api.github.com/gists/${id}`, commonOptions);

    if (response.getResponseCode() !== 200)
      throw new Error(getError(response));

    return new GistInfo(JSON.parse(response.getContentText()));
  }

  this.newGist = function(description, fileName, fileContent) {
    let options = Object.assign({}, commonOptions);

    options.method = "post";
    options.payload = `{
      "description": "${description}",
      "files": {
        "${fileName}": {
          "content": "${fileContent}"
        }
      }
    }`;

    let response = UrlFetchApp.fetch(`https://api.github.com/gists`, options);

    if (response.getResponseCode() !== 201)
      throw new Error(getError(response));

    return new GistInfo(JSON.parse(response));
  }

  this.removeGist = function(id) {
    let options = Object.assign({}, commonOptions);

    options.method = "delete";

    let response = UrlFetchApp.fetch(`https://api.github.com/gists/${id}`, options)

    if (response.getResponseCode() !== 204)
      throw new Error(getError(response));
  }

  this.updateGistDescription = function(id, description) {
    let options = Object.assign({}, commonOptions);

    options.method = "patch";
    options.payload = `{
      "description": "${description}"
    }`;

    let response = UrlFetchApp.fetch(`https://api.github.com/gists/${id}`, options)

    if (response.getResponseCode() !== 200)
      throw new Error(getError(response));

    return new GistInfo(JSON.parse(response.getContentText()));
  }

  this.newGistFile = function(id, fileName, fileContent) {
    let gist = this.getGist(id);
    if (gist.files.filter(file => file.name === fileName).length > 0)
      throw new Error(`File ${fileName} already exists.`);

    let options = Object.assign({}, commonOptions);

    options.method = "patch";
    options.payload = `{
      "files": {
        "${fileName}": {
          "content": "${fileContent}"
        }
      }
    }`;

    let response = UrlFetchApp.fetch(`https://api.github.com/gists/${id}`, options)

    if (response.getResponseCode() !== 200)
      throw new Error(getError(response));

    return new GistInfo(JSON.parse(response.getContentText()));
  }

  this.removeGistFile = function(id, fileName) {
    let gist = this.getGist(id);
    if (gist.files.filter(file => file.name === fileName).length === 0)
      throw new Error(`File ${fileName} doesn't exist.`);

    let options = Object.assign({}, commonOptions);

    options.method = "patch";
    options.payload = `{
      "files": {
        "${fileName}": {
          "content": ""
        }
      }
    }`;

    let response = UrlFetchApp.fetch(`https://api.github.com/gists/${id}`, options)

    if (response.getResponseCode() !== 200)
      throw new Error(getError(response));

    return new GistInfo(JSON.parse(response.getContentText()));
  }

  this.updateGistFile = function(id, fileName, fileContent) {
    let gist = this.getGist(id);
    if (gist.files.filter(file => file.name === fileName).length === 0)
      throw new Error(`File ${fileName} doesn't exist.`);

    let options = Object.assign({}, commonOptions);

    options.method = "patch";
    options.payload = `{
      "files": {
        "${fileName}": {
          "content": "${fileContent}"
        }
      }
    }`;

    let response = UrlFetchApp.fetch(`https://api.github.com/gists/${id}`, options)

    if (response.getResponseCode() !== 200)
      throw new Error(getError(response));

    return new GistInfo(JSON.parse(response.getContentText()));
  }
}

function main() {
  let userName = ScriptProperties.getProperty("user_name");
  let userToken = ScriptProperties.getProperty("user_token");

  let gists = new Gists(new UserInfo(userName, userToken));
  console.log(gists.removeGistFile("c7b5b0170125f6d42b2106ee0a2ed2c5", "Script.sh"));
}