TrigGlobalEfficiencyCorrection: add alternative leg names to MapKeys.cfg

As noted by @tstreble the key name in egamma SF maps for the trigger leg e17_lhvloose_L1EM15VHI does not include the _L1EM15VHI suffix, so updating MapKeys.cfg to make the translation.

EDIT1: and same for e24_lhvloose_L1EM20VH.