Conventions.Remove() in EF Core?

In my regular .NET Framework application, I was using EF 6.x and was also using some Inheritance, specifically:

PurchaseOrder.cs and SaleOrder.cs both inherit from Order.cs

And in the OnModelCreating() on my context class inheriting from IdentityDbContext, I was doing:

modelBuilder.Conventions.Remove<OneToManyCascadeDeleteConvention>();

This used to work, but now I am moving my application to .NET Core 2.0 and I am using EF Core. What achieves the same thing in EF Core? Because right now I am getting the error:

System.Data.SqlClient.SqlException (0x80131904): Introducing FOREIGN KEY constraint 'FK_Order_Business_CustomerId' on table 'Order' may cause cycles or multiple cascade paths. Specify ON DELETE NO ACTION or ON UPDATE NO ACTION, or modify other FOREIGN KEY constraints.

UPDATE

Here's the code after Ahmar's answer. In my context class, I have:

protected override void OnModelCreating(ModelBuilder builder)
{
  base.OnModelCreating(builder);
  builder.HasDefaultSchema("PD");

  builder.Entity<Customer>()
    .HasMany(c => c.SaleOrders)
    .WithOne(e => e.Customer)
    .OnDelete(DeleteBehavior.SetNull);

  builder.Entity<Supplier>()
    .HasMany(po => po.PurchaseOrders)
    .WithOne(e => e.Supplier)
    .OnDelete(DeleteBehavior.SetNull);

  builder.Entity<PurchaseOrder>()
    .HasMany(li => li.LineItems)
    .WithOne(po => po.PurchaseOrder)
    .OnDelete(DeleteBehavior.SetNull);

  builder.Entity<SaleOrder>()
    .HasMany(li => li.LineItems)
    .WithOne(po => po.SaleOrder)
    .OnDelete(DeleteBehavior.SetNull);
}

And as far the Entities, they are:

public abstract class Business : IEntity
{
  protected Business()
  {
    CreatedOn = DateTime.UtcNow;
  }

  public int Id { get; set; }
  public string Name { get; set; }
  public string TaxNumber { get; set; }
  public string Description { get; set; }
  public string Phone { get; set; }
  public string Website { get; set; }
  public string Email { get; set; }
  public bool IsDeleted { get; set; }
  public DateTime CreatedOn { get; set; }
  public DateTime? ModifiedOn { get; set; }
  public ICollection<Address> Addresses { get; set; } = new List<Address>();
  public ICollection<Contact> Contacts { get; set; } = new List<Contact>();
}

[Table("Customers")]
public class Customer : Business
{
  public decimal AllowedCredit { get; set; }
  public decimal CreditUsed { get; set; }
  public int NumberOfDaysAllowedToBeOnMaxedOutCredit { get; set; }
  public ICollection<SaleOrder> SaleOrders { get; set; }
}

[Table("Suppliers")]
public class Supplier : Business
{
  public ICollection<PurchaseOrder> PurchaseOrders { get; set; }
}

public abstract class Order : IEntity
{
  protected Order()
  {
    Date = DateTime.UtcNow;
    CreatedOn = DateTime.UtcNow;
  }

  public int Id { get; set; }
  public DateTime Date { get; set; }
  public decimal ShippingCost { get; set; }
  public Currency ShippingCurrency { get; set; }
  public decimal ShippingConversionRate { get; set; }
  public bool IsDeleted { get; set; }
  public DateTime CreatedOn { get; set; }
  public DateTime? ModifiedOn { get; set; }
  public ICollection<Invoice> Invoices { get; set; }
  public ICollection<Note> Notes { get; set; }
}

[Table("PurchaseOrders")]
public class PurchaseOrder : Order
{
  public int SupplierOrderNumber { get; set; }
  public PurchaseOrderStatus Status { get; set; }
  public decimal Vat { get; set; }
  public decimal ImportDuty { get; set; }
  public int SupplierId { get; set; }
  public Supplier Supplier { get; set; }
  public ICollection<PurchaseOrderLineItem> LineItems { get; set; }
}

[Table("SaleOrders")]
public class SaleOrder : Order
{
  public decimal AmountToBePaidOnCredit { get; set; }
  public SaleOrderStatus Status { get; set; }
  public ICollection<SaleOrderLineItem> LineItems { get; set; }
  public int CustomerId { get; set; }
  public Customer Customer { get; set; }
}

So after doing what Ahmar suggested, I still get the same error when I do update-database.