OvmfPkg: remove the Xen drivers from the IA32, IA32X64, and X64 platforms

OvmfPkg: remove the Xen drivers from the IA32, IA32X64, and X64 platforms

Remove the three Xen drivers as the first step for removing Xen support
from the historical OvmfPkg* platforms. Xen (HVM and PVH) guests are
supported by the dedicated OvmfXen platform.

No module remains dependent on XenHypercallLib, so remove the
XenHypercallLib class resolutions too, from the DSC files.

Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=2122
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Message-Id: <20210526201446.12554-2-lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>