EventUtils: delete some unused algorithms

Frank Winklmeierrequested to merge
fwinkl/athena:eventutils_cleanup into master

Delete unused AddVarAlg+Tool, ParticleCombinerAlg+Tool, ParticleSortingAlg+Tool. These depend on the deprecated IJobOptionsSvc interface. If these algorithms turn out to be useful they can be resurrected and migrated.

Also delete unused MergeContainers.py and cleanup cmake configuration.

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