Remove dependency on build artifacts mirror (#24575)

This reverts #24106.

There was a regression in CircleCI's artifacts API recently where you
could no longer access artifacts without an authorization token. This
broke our size reporting CI job because we can't use an authorization
token on external PRs without potentially leaking it. As a temporary
workaround, I changed the size reporting job to use a public mirror of
our build artifacts.

The CircleCI API has since been fixed to no longer require
authorization, so we can revert the workaround.

.circleci/config.yml

@@ -127,19 +127,22 @@ jobs:
     environment: *environment
     steps:
       - checkout
+      - run: yarn workspaces info | head -n -1 > workspace_info.txt
+      - *restore_node_modules
       - run:
           name: Download artifacts for base revision
-          # TODO: We can't use the normal download-build script here because it
-          # depends on the CircleCI artifacts API, which was recently changed to
-          # require authorization. And we can't pass an authorization token
-          # without possibly leaking it to the public, since we run sizebot on
-          # PRs from external contributors. As a temporary workaround, this job
-          # will pull the artifacts from a public mirror that I set up. But we
-          # should find some other solution so we don't have to maintain
-          # the mirror.
           command: |
-            curl -L --retry 60 --retry-delay 10 --retry-max-time 600 https://react-builds.vercel.app/api/commits/$(git merge-base HEAD origin/main)/artifacts/build.tgz | tar -xz
+              git fetch origin main
+              cd ./scripts/release && yarn && cd ../../
+              scripts/release/download-experimental-build.js --commit=$(git merge-base HEAD origin/main)
               mv ./build ./base-build
+      - run:
+          # TODO: The `download-experimental-build` script copies the npm
+          # packages into the `node_modules` directory. This is a historical
+          # quirk of how the release script works. Let's pretend they
+          # don't exist.
+          name: Delete extraneous files
+          command: rm -rf ./base-build/node_modules
 
       - persist_to_workspace:
           root: .

scripts/release/shared-commands/download-build-artifacts.js

@@ -9,14 +9,6 @@ const {getArtifactsList, logPromise} = require('../utils');
 const theme = require('../theme');
 
 const run = async ({build, cwd, releaseChannel}) => {
-  const CIRCLE_TOKEN = process.env.CIRCLE_CI_API_TOKEN;
-  if (!CIRCLE_TOKEN) {
-    console.error(
-      theme.error('Missing required environment variable: CIRCLE_CI_API_TOKEN')
-    );
-    process.exit(1);
-  }
-
   const artifacts = await getArtifactsList(build);
   const buildArtifacts = artifacts.find(entry =>
     entry.path.endsWith('build.tgz')
@@ -32,7 +24,7 @@ const run = async ({build, cwd, releaseChannel}) => {
   // Download and extract artifact
   await exec(`rm -rf ./build`, {cwd});
   await exec(
-    `curl -L $(fwdproxy-config curl) ${buildArtifacts.url} -H "Circle-Token: ${CIRCLE_TOKEN}" | tar -xvz`,
+    `curl -L $(fwdproxy-config curl) ${buildArtifacts.url} | tar -xvz`,
     {
       cwd,
     }