Revert "Add flag for Assistant feedback UI"

This reverts commit 1a15a88cbbe5f565a3590b4a332d498e83c160cb.

Reason for revert: I believe this is causing a compile failure:
https://ci.chromium.org/buildbot/chromium.chrome/Google%20Chrome%20ChromeOS/61614

Original change's description:
> Add flag for Assistant feedback UI
> 
> 1. Create feature flag for Assistant feedback UI.
> 2. When the flag is set to false, users will use conversation flow
> to send feedback.
> 3. When the flag is set to true, client will open feedback UI for "send
> feedback" query and thumbs down suggestion chip.
> 4. Assistant server will check for this flag and decide whether to start
> feedback conversation flow or send open.url deeplink.
> 
> Bug: b/124127727
> Change-Id: Idcdd6bc1cd4507d0dcc66d8e577c57158c22adaa
> Reviewed-on: https://chromium-review.googlesource.com/c/1461545
> Commit-Queue: Xiao Yang <yanxiao@google.com>
> Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#631461}

TBR=xiaohuic@chromium.org,dmblack@google.com,yanxiao@google.com

Change-Id: I89a84ca642518d66dd0a51f32d3f24461389d072
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: b/124127727
Reviewed-on: https://chromium-review.googlesource.com/c/1469381
Reviewed-by: Katie Dektar <katie@chromium.org>
Commit-Queue: Katie Dektar <katie@chromium.org>
Cr-Commit-Position: refs/heads/master@{#631488}
3 files changed