Comment # 3 on bug 1003381 from Ancor Gonzalez Sosa

Per. Even if it's not possible, the installer is trying to install grub2
because that is what is selected in the "booting" section of the final
installation settings.

If you click on "booting" and select "Not Managed" in the "Boot Loader" field
of the "Boot Loader Settings" screen, grub2 should not be installed. Can you
please try that?