EmbeddedPkg: remove DwEmmcDxe host controller driver

EmbeddedPkg: remove DwEmmcDxe host controller driver

The Synopsys DesignWare eMMC host controller driver does not implement
that SD/MMC host controller protocol that the UEFI spec defines, but an
obsolete EDK2-specific one that predates it. It also does not implement
the UEFI driver model.

Due to this, it has been moved into the edk2-platforms repository,
alongside its remaining users, which have been updated to refer to it in
its new location. So drop this version from EmbeddedPkg.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
Reviewed-by: Philippe Mathieu-Daude <philmd@redhat.com>
Reviewed-by: Leif Lindholm <leif@nuviainc.com>