Revert "[Android] Inflate toolbar stub on a BG thread"

This reverts commit 4f0ac5703fb84e357fd43736589e84b87385f7ee.

Reason for revert: Experiment showed not-so-good results

Original change's description:
> [Android] Inflate toolbar stub on a BG thread
>
> Toolbar inflation currently takes around 200-300ms on the critical path during
> startup. This cl creates the class AsyncViewStub so that the toolbar stub is
> inflated on a background thread outside of the critical path. This leads to an
> improvement of 60ms for startup and 50ms for startup to contentful paint.
>
> Improvements are less than the 200ms being saved due to the remeasure+redraw
> caused by adding new views to the view hierarchy after startup.
>
> Design doc https://docs.google.com/document/d/1lwfhlWqp6os_QhikuqCx60LW5FdSbJ-40Es8ACGd4fI/edit?usp=sharing
>
> Change-Id: I1841f5adbb01a853e952b2e61dedfd4c951e125e
> Bug: 762120
> Reviewed-on: https://chromium-review.googlesource.com/1136797
> Reviewed-by: Ted Choc <tedchoc@chromium.org>
> Commit-Queue: Mohamed Heikal <mheikal@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#584551}


Bug: 762120
Change-Id: I5f85b20a796b8bf5d0bfdd4b8962cf3342700e00
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1519076
Auto-Submit: Mohamed Heikal <mheikal@chromium.org>
Reviewed-by: Ted Choc <tedchoc@chromium.org>
Commit-Queue: Mohamed Heikal <mheikal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#641775}