Revert "[iOS][Alert] Add alert controller to Showcase"

This reverts commit 2410dcb91e53dec59d02a983a5a4c186bc1d854d.

Reason for revert: Bug 954134

Original change's description:
> [iOS][Alert] Add alert controller to Showcase
> 
> Bug: 951301, 951300
> Change-Id: If0af93103f0038ad35770cee09b94b455aeca92b
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1561109
> Commit-Queue: Javier Ernesto Flores Robles <javierrobles@chromium.org>
> Reviewed-by: edchin <edchin@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#652122}

TBR=edchin@chromium.org,javierrobles@chromium.org

Bug: 954134
Change-Id: I4f4d441cf3fa9ea5651a0b0bc01ef41e9bd0f277
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 951301, 951300
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1573639
Reviewed-by: François Doray <fdoray@chromium.org>
Commit-Queue: François Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#652127}
5 files changed