Revert "Enable Assistant for child accounts."

This reverts commit 7c4d25d6e89687033e6234fcf8bb018dee54a193.

Reason for revert: feature punted to M74

Bug: 914210

Original change's description:
> Enable Assistant for child accounts.
>
> This reverts commit 71f820a1783a9ce31f78bea9971c7b4256507bb2 ("Disable assistant for child account").
>
> Bug: b:120075638
> Test: built and tested locally
> Change-Id: I59d3d4869ba596fa462a904b8a64a88230c28325
> Reviewed-on: https://chromium-review.googlesource.com/c/1351155
> Commit-Queue: Henrique Nazaré Santos <nazare@google.com>
> Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
> Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
> Reviewed-by: Sam McNally <sammc@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#613206}

TBR=xiyuan@chromium.org,sammc@chromium.org,xiaohuic@chromium.org,nazare@google.com

Bug: b:120075638
Change-Id: I452fba75870677ec70fc3d1bcec3ab433c5361fd
Reviewed-on: https://chromium-review.googlesource.com/c/1447270
Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Cr-Commit-Position: refs/branch-heads/3683@{#84}
Cr-Branched-From: e51029943e0a38dd794b73caaf6373d5496ae783-refs/heads/master@{#625896}
4 files changed