How did I eliminate my own steel trap as Junkrat?
It's a bug currently present with deployables in Free-For-All Deathmatch. Since there are no teams, a player's own deployables such as Junkrat's trap and Orisa's shield sometimes behave oddly, such as Junkrat's trap being destroyed by his own Concussion Mine and Orisa's shield blocking the pull effect from her alternate fire. There's nothing you can do except wait for a patch to fix it.
This link to Overwatch Patch notes for 1.15 confirms the following bug in FFA;
- Junkrat can destroy his own Steel Trap with a Concussion Mine