Remove the support for booting 'legacy' (i.e., non-UEFI boot) OSes. Contributed-under: TianoCore Contribution Agreement 1.1 Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> Reviewed-by: "Yao, Jiewen" <jiewen.yao@intel.com> Reviewed-by: Achin Gupta <achin.gupta@arm.com>