ArmPlatformPkg: Use the merged Variable driver

ArmPlatformPkg: Use the merged Variable driver

Remove gVariableAuthenticatedRuntimeDxeFileGuid definition in
ArmPlatformPkg.dec and use gVariableRuntimeDxeFileGuid in
NorFlashAuthenticatedDxe.inf as auth Variable driver in SecurityPkg
and Variable driver in MdeModulePkg have been merged.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17768 6f19259b-4bc3-4df7-8a09-765794883524