ArmPkg/AArch64Mmu: remove unused GcdAttributeToArmAttribute()

ArmPkg/AArch64Mmu: remove unused GcdAttributeToArmAttribute()

The function GcdAttributeToArmAttribute() is not used anywhere in the
code base, and is only defined for AARCH64 and not for ARM. It also
fails to set the bits for shareability and non-executability that we
require for correct operation. So remove it.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18888 6f19259b-4bc3-4df7-8a09-765794883524