remove RICH histogram test x86_64_v3 specific ref

Christopher Rob Jonesrequested to merge
remove-rich-hist-v3-ref into master

The x86_64_v3 ref is only needed because of bugs in Gaudi v39r1 in the way the stats are computed, that will be fixed when the master builds move to a newer Gaudi release. For that reason I prefer to remove this ref and live with the diffs until this happens.

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