Revert "Enable kHelpAppV2 by default."

This reverts commit 25d52129.

Reason for revert: Launch being punted to M83.

Original change's description:
> Enable kHelpAppV2 by default.
> 
> For M82.
> Launch bug: https://crbug.com/1042109
> 
> Bug: 1012578
> Change-Id: I76e80ed1f8afc5a34f76fbad30ebef731fd84ff0
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2076738
> Reviewed-by: Alexander Alekseev <alemate@chromium.org>
> Reviewed-by: Trent Apted <tapted@chromium.org>
> Commit-Queue: Rachel Carpenter <carpenterr@google.com>
> Cr-Commit-Position: refs/heads/master@{#744935}

TBR=tapted@chromium.org,alemate@chromium.org,carpenterr@google.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1012578
Change-Id: Ia50fb959b29c97d5e839fd67ecb5a562fadb45d4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2089537Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Commit-Queue: Rachel Carpenter <carpenterr@google.com>
Cr-Commit-Position: refs/heads/master@{#748074}

chromeos/constants/chromeos_features.cc

@@ -174,7 +174,7 @@ const base::Feature kGaiaActionButtons{"GaiaActionButtons",
                                        base::FEATURE_DISABLED_BY_DEFAULT};
 
 // The new ChromeOS Help App. https://crbug.com/1012578.
-const base::Feature kHelpAppV2{"HelpAppV2", base::FEATURE_ENABLED_BY_DEFAULT};
+const base::Feature kHelpAppV2{"HelpAppV2", base::FEATURE_DISABLED_BY_DEFAULT};
 
 // Enable or disable Unified Input Logic for HMM decoder in the IME extension
 // on Chrome OS.