This is easy.
Go into the characters properties and change the following.
Spawn Life: 1
(1 second and the enemy dies.)
Decay Time: 0
(Stops the enemy's body from disappearing.)
Also delete the "male" or "female" from the
Soundset. This will stop the enemy from screaming at the start of the game when they die.
One more thing about this method. If the enemys feet are at ground level (default), when dead the enemy's feet will stick into the ground making them look crunched up like a pile of meat. Make sure you use the "Page Up" key to raise the enemy further up into the air. The problem is, no matter what angle you make the enemy start at, they will ragdoll the same (stood up). I wish they would fix this. This mean you can't lie them down on a table and have them ragdoll, sorry.