Add security net logging for guest uninstall of updates.

This adds security net logging for the fix added in ag/17352264,
which prevents a non-admin user from uninstalling updates to
system apps.

Bug: 170646036
Test: run scenario and check log
Change-Id: I3546d028ca421271b323987bb1761040dab17c10

services/core/java/com/android/server/pm/DeletePackageHelper.java

@@ -167,6 +167,7 @@ final class DeletePackageHelper {
                 if (userInfo == null || !userInfo.isAdmin()) {
                     Slog.w(TAG, "Not removing package " + packageName
                             + " as only admin user may downgrade system apps");
+                    EventLog.writeEvent(0x534e4554, "170646036", -1, packageName);
                     return PackageManager.DELETE_FAILED_USER_RESTRICTED;
                 }
             }