message: [gatsby-plugin-vercel-builder] Remove `vercel.config.js` file handling
diff: import { join } from 'path';
  import { getTransformedRoutes } from '@vercel/routing-utils';
  -import { pathExists, writeJson, remove } from 'fs-extra';
  +import { writeJson, remove } from 'fs-extra';
  import { validateGatsbyState } from './schemas';
  import {
  createServerlessFunctions,
  @@ -68,11 +68,6 @@ export async function generateVercelBuildOutputAPI3Output({
  await Promise.all(createPromises);
  - const vercelConfigPath = `${process.cwd()}/vercel.config.js`;
  - const vercelConfig: Config = (await pathExists(vercelConfigPath))
  - ? require(vercelConfigPath).default
  - : {};
  -
  let trailingSlash: boolean | undefined = undefined;
  if (gatsbyConfig.trailingSlash === 'always') {
  @@ -82,7 +77,6 @@ export async function generateVercelBuildOutputAPI3Output({
  }
  const { routes } = getTransformedRoutes({
  - ...vercelConfig,
  trailingSlash,
  redirects: redirects.map(({ fromPath, toPath, isPermanent }) => ({
  source: fromPath,
  