removes remaining back office things from underlying UmbracoUserManager moves files

src/Umbraco.Infrastructure/Security/BackOfficeUserValidator.cs

@@ -0,0 +1,20 @@
+using System.Threading.Tasks;
+using Microsoft.AspNetCore.Identity;
+using Umbraco.Core.Security;
+
+namespace Umbraco.Core.Security
+{
+    public class BackOfficeUserValidator<T> : UserValidator<T>
+        where T : BackOfficeIdentityUser
+    {
+        public override async Task<IdentityResult> ValidateAsync(UserManager<T> manager, T user)
+        {
+            // Don't validate if the user's email or username hasn't changed otherwise it's just wasting SQL queries.
+            if (user.IsPropertyDirty("Email") || user.IsPropertyDirty("UserName"))
+            {
+                return await base.ValidateAsync(manager, user);
+            }
+            return IdentityResult.Success;
+        }
+    }
+}