Switch TRT_PAI_Process ToolHandles owned by TRTDigitizationTool to be private

John Derek Chapmanrequested to merge
jchapman/athena:PrivateTRT_PAITools_master into master

This merge request switches the TRT_PAI_Process ToolHandles owned by TRTDigitizationTool to be private.
It also cleans up the configurations of the TRT_PAI_Process tools, so that they are no longer added to the ToolSvc.

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