tweak model ShelfLogEntry, step 1/2

journal/models.py

@@ -518,9 +518,6 @@ class Shelf(List):
 
 class ShelfLogEntry(models.Model):
     owner = models.ForeignKey(User, on_delete=models.PROTECT)
-    shelf = models.ForeignKey(
-        Shelf, on_delete=models.CASCADE, related_name="entries", null=True
-    )  # None means removed from any shelf
     shelf_type = models.CharField(choices=ShelfType.choices, max_length=100, null=True)
     item = models.ForeignKey(Item, on_delete=models.PROTECT)
     timestamp = models.DateTimeField(
@@ -596,7 +593,6 @@ class ShelfManager:
             ShelfLogEntry.objects.create(
                 owner=self.owner,
                 shelf_type=shelf_type,
-                shelf=shelf,
                 item=item,
                 metadata=metadata,
             )