Remove globalTimeOffset getter and GlobalTimeOffset property from GaudiCommon

GaudiCommon adds a property GlobalTimeOffset and a corresponding getter
globalTimeOffset to every algorithm/tool which uses GaudiCommon,
regardless on whether this property is used.

As there is no code anymore that actually uses globalTimeOffset, this
patch removes this accessor and the corresponding property.

Fixes GAUDI-1122.

See merge request !61