Platform/ARM/BdsLib: drop unused functions

Clean up BdsLib (which is deprecated and should not be used for future
development) by removing all the pieces that are not being used at the
moment.

After this patch, only BdsLoadImage() remains, and the pieces it relies
upon. This function is used by FdtPlatformDxe to load device tree
binaries from device paths.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Thomas Abraham <thomas.abraham@arm.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>