Scripts/Pit of Saron: Changed Overlord's Brand script to be safer

Closes #9125
Scripts/Quest: Fix "Massacre At Light's" after recent vehicle changes and drop some silly code

Closes #9448
Merge pull request #9632 from joschiwald/scriptfix

Scripts/Quest: Fix "Massacre At Light's" after recent vehicle changes an...
Script/SAI: Remove Shadow's Edge on completing 'Shadowmourne...'

Closes: #9600