don't show "member added" info-messages in channels

[adbenitez]

in Telegram nothing is shown in-chat when someone joins a channel, you see the subscribers counter in the title bar, and can see the member list in the chat profile

currently in Delta Chat we are adding an info-message every time someone joins, this results in the chat looking like this:

for an start, these messages look a bit clumsy / not idiomatic, "foo joined the channel" would be more appropriate, but it would be better to just not add such events as in-chat info-messages for channels, they just clutter the chat timeline, better do like Telegram

[r10s]

to add, there us the number of subscribers, which already gives a good-enough idea.

and, we would probably want to hide the "member removed" info as well, it is not adding much.

with that, channel owner can concentrate more on their content, and have a view similat to the subscribers - and not messages teared apart hugely.

(for smaller channels, the hints may be more interesting, but there, probably often enough groups are the better tool. also, currently, you can always watch the profile to check subscribers, esp if you expect few only) (finally, the removal of the info-messages makes channel owner less used to "who is subscribing"; there are ideas around to always subscribe more incognito (however that can be done, this discussion is out of scope))