Revert "Enable migration from default Chrome apps to default web apps"

This reverts commit 6545f679.

Reason for revert: crbug.com/1154558

Original change's description:
> Enable migration from default Chrome apps to default web apps
>
> This CL enables the migration from default installed Chrome apps to
> default installed web apps.
>
> This still needs feature launch approval:
>  - Chrome OS: https://crbug.com/1099150
>  - Desktop: https://crbug.com/1130075
> This migration is being enabled to get test coverage and user reports
> in canary.
> If this is not approved by branch point it will be disabled again.
>
> Test: ExternalWebAppMigrationBrowserTest
> Bug: 1058265, 809304
> Change-Id: I22f8b43631708a40b5333a7ce1bd4177e9792b49
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2562922
> Reviewed-by: Glen Robertson <glenrob@chromium.org>
> Commit-Queue: Alan Cutter <alancutter@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#832669}

TBR=alancutter@chromium.org,chromium-scoped@luci-project-accounts.iam.gserviceaccount.com,glenrob@chromium.org

Change-Id: I4ee2e3b938bfc9cc434c025fb9b0b01776d20199
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1058265
Bug: 809304
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2568995Reviewed-by: Hajime Hoshi <hajimehoshi@chromium.org>
Commit-Queue: Hajime Hoshi <hajimehoshi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#832713}

chrome/browser/web_applications/components/external_app_install_features.cc

@@ -25,13 +25,14 @@ bool g_always_enabled_for_testing = false;
 // Enables migration of default installed GSuite apps over to their replacement
 // web apps.
 const base::Feature kMigrateDefaultChromeAppToWebAppsGSuite{
-    "MigrateDefaultChromeAppToWebAppsGSuite", base::FEATURE_ENABLED_BY_DEFAULT};
+    "MigrateDefaultChromeAppToWebAppsGSuite",
+    base::FEATURE_DISABLED_BY_DEFAULT};
 
 // Enables migration of default installed non-GSuite apps over to their
 // replacement web apps.
 const base::Feature kMigrateDefaultChromeAppToWebAppsNonGSuite{
     "MigrateDefaultChromeAppToWebAppsNonGSuite",
-    base::FEATURE_ENABLED_BY_DEFAULT};
+    base::FEATURE_DISABLED_BY_DEFAULT};
 
 bool IsExternalAppInstallFeatureEnabled(base::StringPiece feature_name) {
   if (g_always_enabled_for_testing)