[illink] Delete RemoveAttributesBase (#11061)

`Microsoft.Android.Sdk.ILLink` still carried `RemoveAttributesBase` even though nothing in the project derives from or references it. This change removes the dead linker substep to keep the ILLink surface smaller and easier to navigate.

Co-authored-by: sbomer <787361+sbomer@users.noreply.github.com>

Author: Copilot