Update to photon isolation systematics in AT

It looks like the prescriptions used in AT for the systematics on the photon isolation efficiency were quite outdated (r20.7, early r21). This MR implements weight_photonSF_effIso_UP and weight_photonSF_effIso_DOWN, to be used instead of the weight_photonSF_effLowPtIso_ and weight_photonSF_effTrkIso_ variations.

Waiting for confirmation from IFF. Could also remove the LowPt and Trk isolations if they're indeed not needed anymore.

Thanks to @oducu for the confirmation 🙂 Also removed the LowPt, Trk and DDonoff isolations (obsolete).