Revert "[iOS][follow-entry] Add coordinator for the following feed overlay"

This reverts commit e4eb6c639684e01ff44360a0e48f17641d8f1281.

Reason for revert: Project cancelled

Original change's description:
> [iOS][follow-entry] Add coordinator for the following feed overlay
>
> This CL adds the coordinator and a placeholder view controller for the
> following feed overlay.
>
> https://screenshot.googleplex.com/9MsbcKmEiHiNzFZ
>
> Bug: 359325090
> Change-Id: Ie657915d255d172d5e098dfebf351e2322557ee9
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6158485
> Auto-Submit: Ginny Huang <ginnyhuang@chromium.org>
> Reviewed-by: Chris Lu <thegreenfrog@chromium.org>
> Commit-Queue: Chris Lu <thegreenfrog@chromium.org>
> Commit-Queue: Ginny Huang <ginnyhuang@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1404461}

Bug: 359325090
Change-Id: I335ee956c887ff95d33a959b5c0dee1d03898441
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6216689
Reviewed-by: Scott Yoder <scottyoder@google.com>
Commit-Queue: Ginny Huang <ginnyhuang@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1414963}