ArmPkg/ArmLib: remove all ArmLib flavors except ArmBaseLib

This removes the following ArmLib implementation, which were, apart from
the fact that they targeted either ARM or AARCH64, fully identical:

  ArmPkg/Library/ArmLib/AArch64/AArch64Lib.inf
  ArmPkg/Library/ArmLib/AArch64/AArch64LibPei.inf
  ArmPkg/Library/ArmLib/AArch64/AArch64LibPrePi.inf
  ArmPkg/Library/ArmLib/AArch64/AArch64LibSec.inf
  ArmPkg/Library/ArmLib/ArmV7/ArmV7Lib.inf
  ArmPkg/Library/ArmLib/ArmV7/ArmV7LibPrePi.inf
  ArmPkg/Library/ArmLib/ArmV7/ArmV7LibSec.inf

Only ArmBaseLib remains, which can fulfil the dependencies upon each of
the listed flavors.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>