fix #M132 - Sunsword glows after its wielder dies

fix #M132 - Sunsword glows after its wielder dies

     When lit due to being wielded by a monster, Sunsword continued to emit
light after that monster was killed.  This was fixed by <Someone> in 3.4.1 but a
change I made for 3.4.3 broke that fix.  When mdrop_obj() was split out of
relobj(), relevant unwielding code ended up only being executed for monsters
who were still alive.