Provides a solution to the regression introduced by 1c373b66, which removed passing of hard-coded kill types to on_killedplayer callbacks, and passed the wielditem instead.
The problem with passing wielditem is that throwables can't be detected, as the wielditem would be nil. Grenades used to be detected before the aforementioned commit due to the special `grenade` damage group in the grenade's toolcaps.
769b278494