Enable by default the feature that removes programmatic auth usage from Chrome.

This CL also enables the feature to remove the programmatic auth endpoint
from Chrome. The plan is to continue to use the finch experiment as a kill
switch in case we discover any issues with the server-side signin pages.

For more info, please relate to
https://bugs.chromium.org/p/chromium/issues/detail?id=780808#c20

Bug: 780808
Change-Id: I786b21fcbb041fb9266e5fdfe8a42e98f3942e7f
Reviewed-on: https://chromium-review.googlesource.com/793690
Commit-Queue: Mihai Sardarescu <msarda@chromium.org>
Reviewed-by: David Roger <droger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#520145}

chrome/common/chrome_features.cc

@@ -455,7 +455,7 @@ const base::Feature kPwaMinimalUi{"PwaMinimalUi",
 #if !defined(OS_ANDROID)
 const base::Feature kRemoveUsageOfDeprecatedGaiaSigninEndpoint{
     "RemoveUsageOfDeprecatedGaiaSigninEndpoint",
-    base::FEATURE_DISABLED_BY_DEFAULT};
+    base::FEATURE_ENABLED_BY_DEFAULT};
 #endif
 
 #if defined(OS_CHROMEOS)