OvmfPkg/Virtio: Removed VirtioReadDevice() / VirtIoWriteDevice() functions

OvmfPkg/Virtio: Removed VirtioReadDevice() / VirtIoWriteDevice() functions

These functions did not provide much more than the new protocol functions
VIRTIO_DEVICE_PROTOCOL.ReadDevice() / VIRTIO_DEVICE_PROTOCOL.WriteDevice().

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Olivier Martin <olivier.martin@arm.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@14968 6f19259b-4bc3-4df7-8a09-765794883524