[HL2MP] Fix external prop influence

[speedvoltage]

Issue: Whenever player 1 tags an explosive prop e.g. uses their pistol to shoot one bullet on an explosive oil drum, which doesn't set it on fire, that barrel has that player 1 as the owner, no matter what happens next. Therefore if that prop is used in the future by player 2 and kills player 3, then player 1 gets the point/frag because the game assumes they are the one who made the kill and shows so in the death notice.

Fix: Reset prop ownership after 2 seconds if it was not manipulated by anyone after the last interaction.