You just need the butcher knife to kill tamed animals, you don't need to enable friendly fire.

I think maybe you need to use a butcher knife now, crafted from wood and tin.

open your inventory ( tab ) and in the top right corner you can deselect friendly fire.
when you do this you can do damage to your boars and other players.
If im not mistaken, then you also need a special knife to kill them. ( i cant remember the name of it )

you need toggle ff on to attack tamed animals now

from invnetory, swords button on top right