CFElements: use isRun3Cfg for legacy support

Frank Winklmeier requested to merge fwinkl/athena:fwinkl_20220406T191604 into 22.0

Use ComponentFactory.isRun3Cfg to check if we are in legacy configurable mode. This is more general than configurableRun3Behavior and ensures that the same logic is used as in CompFactory.

Also remove the use of the __future__ module and cleanup cmake configuration.

Edited by Frank Winklmeier

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