When was mining removed from Bitcoin Core? I don't see it removed.
Anyways, I don't think that it will be removed since mining code is required for testnet and regtest. It would be a little pointless to change it to only be able to mine on the test networks and not the mainnet as that just adds extra code. However it could be removed from the mainnet code since there really is no point in attempting to solo cpu mine Bitcoin.
It was removed from the GUI some years ago, I think that's what he meant.