Medical Status - Fix double execution of killed event

[commy2]

When merged this pull request will:

• replace close fix double execution of killed event #7531
• close ACE Arsenal VR Targets duplicating when killed #7185
• close Server not counting killsInfantry #3111
• Copies the fix for Object Killed event to the Mission Killed event (a.k.a. EntityKilled, which is a terrible name for a non entity=mission event...).

bob1 addEventHandler ["Killed", { 
    systemChat str ["Object Killed", _this]; 
}];

addMissionEventHandler ["EntityKilled", { 
    systemChat str ["Mission Killed", _this]; 
}];

Note that execNextFrame is how we killed units pre rewrite. The biggest issue was incorrect returns, but Pabst solved that independently and removed my reason for moving setDamage into HandleDamage in the first place.

Secondary execution runs with null objects. Should dedmen fix https://feedback.bistudio.com/T149510, the issue will be gone.