Remove some dead code from MessageModel::createEventObjects

This senderId variable doesn't seem to be used in the current iteration
of this function, lets remove it.

src/timeline/models/messagemodel.cpp

@@ -426,15 +426,9 @@ void MessageModel::createEventObjects(const Quotient::RoomEvent *event)
     }
 
     auto eventId = event->id();
-    auto senderId = event->senderId();
     if (eventId.isEmpty()) {
         eventId = event->transactionId();
     }
-    // A pending event might not have a sender ID set yet but in that case it must
-    // be the local member.
-    if (senderId.isEmpty()) {
-        senderId = m_room->localMember().id();
-    }
 
     // ReadMarkerModel handles updates to add and remove markers, we only need to
     // handle adding and removing whole models here.