ArmPkg: drop ArmBds remnant Pcds from .dec

ArmPkg: drop ArmBds remnant Pcds from .dec

The following Pcds
- gArmTokenSpaceGuid.PcdArmLinuxSpinTable
- gArmTokenSpaceGuid.PcdArmLinuxAtagMaxOffset
- gArmTokenSpaceGuid.PcdArmLinuxFdtMaxOffset
- gArmTokenSpaceGuid.PcdArmLinuxFdtAlignment
remained defined, without actual users.
So get rid of them.

One reference to be deleted separately from edk2-platforms.

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>