Remove old todo for support of draft to broadcasting transition

It looks like we were allowing broadcasts to transition from draft to
broadcasting in one go. This isn't valid now. It should go draft,
pending approval and then broadcasting.

It looks like this was a leftover bit of support in our code for when we
were building stuff out and is no longer needed.

app/models.py

@@ -2218,10 +2218,7 @@ class BroadcastStatusType(db.Model):
 
     # these are only the transitions we expect to administer via the API code.
     ALLOWED_STATUS_TRANSITIONS = {
-        DRAFT: {
-            PENDING_APPROVAL,
-            BROADCASTING,  # TODO: Remove me once we have pending approval flow put in properly
-        },
+        DRAFT: {PENDING_APPROVAL},
         PENDING_APPROVAL: {REJECTED, DRAFT, BROADCASTING},
         REJECTED: {DRAFT, PENDING_APPROVAL},
         BROADCASTING: {COMPLETED, CANCELLED},