Set sealed property for a site column using CSOM (Delete a sealed site column sharepoint online)

There are some site columns create in our sharepoint online site which were created using the client side object model (csom) with the "Sealed" property set to True.

I now want to delete these columns, but I am unable to do so using the csom as a result of the column being sealed.

I have tried to update the field to set the Sealed property to false on the site column, but get an error, and looking at the definition of the property (https://msdn.microsoft.com/EN-US/library/microsoft.sharepoint.client.field.sealed.aspx), it appears to be read only.

Can anyone tell me how to update the sealed property of a site column in sharepoint online using the client side object model?

Thanks in advance for any assistance!