ArmVirtPkg: drop ArmPlatformGlobalVariableLib dependency

ArmVirtPkg: drop ArmPlatformGlobalVariableLib dependency

Now that all PeiServicesTablePointerLib and PrePiHobListPointerLib
library dependencies in both ArmVirtQemu and ArmVirtXen are satisfied
by implementations that do not depend on ArmPlatformGlobalVariableLib,
we can remove all mention of it from the various .dsc files.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18986 6f19259b-4bc3-4df7-8a09-765794883524