xAOD::EventAuxInfo_v3 Converter Fix, 21.0-mc16a branch (2021.12.07.)

Taught the xAOD::EventAuxInfo POOL converter about the v3->v1 converter tool. Which I forgot doing in !48800 (merged). 😦

This is yet another step towards fixing ATLASRECTS-6707, and a direct fix for ATR-24697. It is also a twin of !48887 (merged).