Delete ITrigMessageSvc interface

Frank Winklmeierrequested to merge
fwinkl/athena:trigmsgsvc_outputlevel into master

The ITrigMessageSvc interface only provided one additional method (resetOutputLevels) that is no longer needed/used. Delete this interface and its dictionary. Since the latter was the only remaining purpose of the TrigPython package, delete this package (cf ATR-19150).

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