GlobalTag.py: remove misleading print out

Do not print the global tag after expanding it.
This was both misleading (users overriding the global tag would still see the wrong print out) and not in line with the CMSSW practices (messages should be printed via the MessageLogger, not directly to the standard output).
Merge pull request #4336 from fwyzard/GlobalTag_remove_printout

GlobalTag.py: remove misleading print out