Stop calling UseIdentity since it is the default anyway

src/Microsoft.AspNet.Identity.EntityFramework/IdentityDbContext.cs

@@ -26,10 +26,6 @@ namespace Microsoft.AspNet.Identity.EntityFramework
 
         protected override void OnModelCreating(ModelBuilder builder)
         {
-            // TODO: Temporary change. 
-            // Can be reverted once https://github.com/aspnet/EntityFramework/issues/2175 is closed
-            builder.ForSqlServer().UseIdentity();
-
             builder.Entity<TUser>(b =>
                 {
                     b.Key(u => u.Id);