sandbox: Drop special case console code for sandbox

At present sandbox has a special case where it directly calls os_putc()
when it does not have a console yet.

Now that we have the pre-console buffer enabled we can drop this. Any
early characters will be buffered and output later.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Stephen Warren <swarren@nvidia.com>