ci(docs-infra): remove redundant standalone ngcc run (#36145)

Previously, in the `test_aio` CI job, we ran ngcc before building the
app with `yarn build`. This was supposed to have the benefit of taking
advantage of the parallel capabilities of standalone ngcc (vs implicitly
running it via `ng build`).

It turns out that the work done by the standalone ngcc was thrown away
before the `ng build`, resulting in `ng build` having to run ngcc all
over again. This happened because the `yarn build` script (run after the
standalone ngcc step) also runs `yarn install`, which essentially cleans
up `node_modules/`, thus discarding all the work already done by ngcc.

Here is an [example CI job][1], where this can be seen in action:
One can see the "Compiling <some-package> : es2015 as esm2015" logs in
the `yarn --cwd aio ngcc --properties es2015` step (as the standalone
ngcc processes the various entry-points) and then see the same logs in
the `yarn --cwd aio build --progress=false` step (as ngcc has to process
the entry-points all over again).

This commit removes the redundant standalone ngcc run and lets the CLI
handle ngcc via `ng build`. It is possible to instrument the build
process in a way that we can run the standalone ngcc after
`yarn install` and thus take advantage of the performance gains in
parallel mode, but the latest version of the CLI can already run ngcc in
parallel mode as a pre-build step, so this is unnecessary.

[1]: https://circleci.com/gh/angular/angular/658691

PR Close #36145

.circleci/config.yml

@@ -384,10 +384,6 @@ jobs:
       - custom_attach_workspace
       - init_environment
       - install_chrome_libs
-        # Compile dependencies to ivy
-        # Running `ngcc` here (instead of implicitly via `ng build`) allows us to take advantage of
-        # the parallel, async mode speed-up (~20-25s on CI).
-      - run: yarn --cwd aio ngcc --properties es2015
         # Build aio
       - run: yarn --cwd aio build --progress=false
         # Lint the code