Inline get_recipient_user_ids() into two callers.

This sets us up a subsequent commit where we need more data
from the Subscription table to build recipient info, so the
function boundary doesn't work any more for get_recipient_info,
which is part of the heavily optimized send-message
path.

We used to share code here with typing notifications, but
typing notifications need a lot less data than the
send-message path, so it's useful to decouple these two
things.  The idioms that are duplicated here are pretty simple
one-liners.

zerver/lib/actions.py

@@ -714,24 +714,6 @@ def render_incoming_message(message, content, user_ids, realm):
         raise JsonableError(_('Unable to render message'))
     return rendered_content
 
-def get_recipient_user_ids(recipient, sender_id):
-    # type: (Recipient, int) -> List[int]
-    if recipient.type == Recipient.PERSONAL:
-        # The sender and recipient may be the same id, so
-        # de-duplicate using a set.
-        user_ids = list({recipient.type_id, sender_id})
-        assert(len(user_ids) in [1, 2])
-        return user_ids
-
-    elif (recipient.type == Recipient.STREAM or recipient.type == Recipient.HUDDLE):
-        user_ids = Subscription.objects.filter(
-            recipient=recipient,
-            active=True,
-        ).order_by('user_profile_id').values_list('user_profile_id', flat=True)
-        return user_ids
-
-    raise ValueError('Bad recipient type')
-
 def get_typing_user_profiles(recipient, sender_id):
     # type: (Recipient, int) -> List[UserProfile]
     if recipient.type == Recipient.STREAM:
@@ -742,7 +724,21 @@ def get_typing_user_profiles(recipient, sender_id):
         '''
         raise ValueError('Typing indicators not supported for streams')
 
-    user_ids = get_recipient_user_ids(recipient, sender_id)
+    if recipient.type == Recipient.PERSONAL:
+        # The sender and recipient may be the same id, so
+        # de-duplicate using a set.
+        user_ids = list({recipient.type_id, sender_id})
+        assert(len(user_ids) in [1, 2])
+
+    elif recipient.type == Recipient.HUDDLE:
+        user_ids = Subscription.objects.filter(
+            recipient=recipient,
+            active=True,
+        ).order_by('user_profile_id').values_list('user_profile_id', flat=True)
+
+    else:
+        raise ValueError('Bad recipient type')
+
     users = [get_user_profile_by_id(user_id) for user_id in user_ids]
     return users
 
@@ -757,7 +753,26 @@ RecipientInfoResult = TypedDict('RecipientInfoResult', {
 
 def get_recipient_info(recipient, sender_id):
     # type: (Recipient, int) -> RecipientInfoResult
-    user_ids = get_recipient_user_ids(recipient, sender_id)
+    if recipient.type == Recipient.PERSONAL:
+        # The sender and recipient may be the same id, so
+        # de-duplicate using a set.
+        user_ids = list({recipient.type_id, sender_id})
+        assert(len(user_ids) in [1, 2])
+
+    elif recipient.type == Recipient.STREAM:
+        user_ids = Subscription.objects.filter(
+            recipient=recipient,
+            active=True,
+        ).order_by('user_profile_id').values_list('user_profile_id', flat=True)
+
+    elif recipient.type == Recipient.HUDDLE:
+        user_ids = Subscription.objects.filter(
+            recipient=recipient,
+            active=True,
+        ).order_by('user_profile_id').values_list('user_profile_id', flat=True)
+
+    else:
+        raise ValueError('Bad recipient type')
 
     query = UserProfile.objects.filter(
         id__in=user_ids