notification bot: Modify initial stream creation message.

Discussion at
https://chat.zulip.org/#narrow/stream/137-feedback/topic/hello.20topic

The "by @**X**" part in the message content is in a later commit.

tools/lib/capitalization.py

@@ -121,7 +121,7 @@ IGNORED_PHRASES = [
     # We should probably just delete this string from translations
     r'activation key',
     # this is used as a topic
-    r'^hello$',
+    r'^stream events$',
     # These are used as example short names (e.g. an uncapitalized context):
     r"^marketing$",
     r"^cookie$",

zerver/lib/actions.py

@@ -1709,20 +1709,11 @@ def check_typing_notification(sender: UserProfile,
     assert recipient.type != Recipient.STREAM
     return {'sender': sender, 'recipient': recipient, 'op': operator}
 
-def stream_welcome_message(stream: Stream) -> str:
-    content = _('Welcome to #**%s**.') % (stream.name,)
-
-    if stream.description:
-        content += '\n\n**' + _('Description') + '**: '
-        content += stream.description
-
-    return content
-
 def prep_stream_welcome_message(stream: Stream) -> Optional[Dict[str, Any]]:
     realm = stream.realm
-    sender = get_system_bot(settings.WELCOME_BOT)
-    topic = _('hello')
-    content = stream_welcome_message(stream)
+    sender = get_system_bot(settings.NOTIFICATION_BOT)
+    topic = _('stream events')
+    content = _('Stream created. Welcome!')
 
     message = internal_prep_stream_message(
         realm=realm,

zerver/tests/test_subs.py

@@ -57,7 +57,6 @@ from zerver.lib.actions import (
     ensure_stream,
     do_deactivate_stream,
     do_deactivate_user,
-    stream_welcome_message,
     do_create_default_stream_group,
     do_add_streams_to_default_stream_group, do_remove_streams_from_default_stream_group,
     do_remove_default_stream_group,
@@ -240,32 +239,6 @@ class TestCreateStreams(ZulipTestCase):
         self.assertFalse(stream.invite_only)
         self.assertFalse(stream.history_public_to_subscribers)
 
-    def test_welcome_message(self) -> None:
-        realm = get_realm('zulip')
-        name = u'New Stream'
-
-        new_stream = ensure_stream(
-            realm=realm,
-            stream_name=name
-        )
-        welcome_message = stream_welcome_message(new_stream)
-
-        self.assertEqual(
-            welcome_message,
-            u'Welcome to #**New Stream**.'
-        )
-
-        new_stream.description = 'Talk about **stuff**.'
-
-        welcome_message = stream_welcome_message(new_stream)
-
-        self.assertEqual(
-            welcome_message,
-            'Welcome to #**New Stream**.'
-            '\n\n'
-            '**Description**: Talk about **stuff**.'
-        )
-
 class RecipientTest(ZulipTestCase):
     def test_recipient(self) -> None:
         realm = get_realm('zulip')
@@ -2334,9 +2307,9 @@ class SubscriptionAPITest(ZulipTestCase):
         # verify that a welcome message was sent to the stream
         msg = self.get_last_message()
         self.assertEqual(msg.recipient.type, msg.recipient.STREAM)
-        self.assertEqual(msg.topic_name(), u'hello')
-        self.assertEqual(msg.sender.email, settings.WELCOME_BOT)
-        self.assertIn('Welcome to #**', msg.content)
+        self.assertEqual(msg.topic_name(), u'stream events')
+        self.assertEqual(msg.sender.email, settings.NOTIFICATION_BOT)
+        self.assertEqual('Stream created. Welcome!', msg.content)
 
     def test_multi_user_subscription(self) -> None:
         user1 = self.example_user("cordelia")