Deprecate proto for policy SupervisedUsersEnabled.

This CL marks the proto for the deprecated device policy SupervisedUsersEnabled as deprecated. The policy SupervisedUsersEnabled has already been deprecated in CL 1221253 and the code for reading from the proto SupervisedUsersSettingsProto was removed in the CL 1224033.

Bug: 834488
Change-Id: I067708d9e3eb1defb5b92b9c1276a39998316495
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2038773Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Sergey Poromov <poromov@chromium.org>
Commit-Queue: Saurabh Nijhara <snijhara@google.com>
Cr-Commit-Position: refs/heads/master@{#739020}

chrome/browser/chromeos/ownership/owner_settings_service_chromeos.cc

@@ -458,14 +458,6 @@ void OwnerSettingsServiceChromeOS::UpdateDeviceSettings(
       guest->set_guest_mode_enabled(guest_value);
     else
       NOTREACHED();
-  } else if (path == kAccountsPrefSupervisedUsersEnabled) {
-    em::SupervisedUsersSettingsProto* supervised =
-        settings.mutable_supervised_users_settings();
-    bool supervised_value;
-    if (value.GetAsBoolean(&supervised_value))
-      supervised->set_supervised_users_enabled(supervised_value);
-    else
-      NOTREACHED();
   } else if (path == kAccountsPrefShowUserNamesOnSignIn) {
     em::ShowUserNamesOnSigninProto* show = settings.mutable_show_user_names();
     bool show_value;
@@ -639,6 +631,7 @@ void OwnerSettingsServiceChromeOS::UpdateDeviceSettings(
   } else {
     // The remaining settings don't support Set(), since they are not
     // intended to be customizable by the user:
+    //   kAccountsPrefSupervisedUsersEnabled
     //   kAccountsPrefTransferSAMLCookies
     //   kDeviceAttestationEnabled
     //   kDeviceOwner

components/policy/proto/chrome_device_policy.proto

@@ -843,9 +843,9 @@ message AccessibilitySettingsProto {
   optional PolicyOptions login_screen_shortcuts_enabled_options = 35;
 }
 
-message SupervisedUsersSettingsProto {
+message OBSOLETE_SupervisedUsersSettingsProto {
   // Defines whether supervised users can be created on the device.
-  optional bool supervised_users_enabled = 1;
+  optional bool OBSOLETE_supervised_users_enabled = 1 [deprecated = true];
 }
 
 message LoginScreenPowerManagementProto {
@@ -1591,7 +1591,8 @@ message ChromeDeviceSettingsProto {
   optional VariationsParameterProto variations_parameter = 25;
   optional AttestationSettingsProto attestation_settings = 26;
   optional AccessibilitySettingsProto accessibility_settings = 27;
-  optional SupervisedUsersSettingsProto supervised_users_settings = 28;
+  optional OBSOLETE_SupervisedUsersSettingsProto supervised_users_settings = 28
+      [deprecated = true];
   optional LoginScreenPowerManagementProto login_screen_power_management = 29;
   optional SystemUse24HourClockProto use_24hour_clock = 30;
   optional AutoCleanupSettigsProto auto_clean_up_settings = 31;