Deletes the mobile tab of the "Forward message" section as that is not a named feature in the mobile app. Adds a tip about setting a different topic if the user is in the channel view of the mobile app. Part of #34748.
Signed-off-by: Anders Kaseorg <anders@zulip.com>
Move the page to /help/quote-or-forward-a-message and add a url redirect from the old url. Fixes #31953
