ArmVirtPkg/ArmVirtQemu: Revert "limit ACPI support to v5.0 and higher"

This reverts commit e0692789.

The default value for PcdAcpiExposedTableVersions is now set to 0x20
for Aarch64 systems. Setting this PCD in ArmVirtPkg/ArmVirtQemu.dsc
is no longer necessary.

Signed-off-by: Samer El-Haj-Mahmoud <samer@elhajmahmoud.com>
Acked-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>