Initial side by side implementation

src/Umbraco.Web/Security/BackOfficeSignInManager.cs

@@ -16,19 +16,6 @@ using Constants = Umbraco.Core.Constants;
 
 namespace Umbraco.Web.Security
 {
-    // TODO: SB: Create new custom BackOfficeSignInManager2 (rename pending)
-    public class BackOfficeSignInManager2
-    {
-        // Create
-        // CreateUserIdentityAsync
-        // PasswordSignInAsync
-        // SignInAsync
-        // GetVerifiedUserIdAsync
-        // GetVerifiedUserNameAsync
-        // TwoFactorSignInAsync
-        // SendTwoFactorCodeAsync
-    }
-
     // TODO: In v8 we need to change this to use an int? nullable TKey instead, see notes against overridden TwoFactorSignInAsync
     public class BackOfficeSignInManager : SignInManager<BackOfficeIdentityUser, int>
     {