api: deprecate webxdc descr parameter (#6255)

this PR removes most usages of the `descr` parameter.

- to avoid noise in different branches etc. (as annoying on similar, at
a first glance simple changes), i left the external API stable

- also, the effort to do a database migration seems to be over the top,
so the column is left and set to empty strings on future updates - maybe
we can recycle the column at some point ;)

closes #6245

deltachat-repl/src/cmdline.rs

@@ -969,9 +969,7 @@ pub async fn cmdline(context: Context, line: &str, chat_id: &mut ChatId) -> Resu
                 "Arguments <msg-id> <json status update> expected"
             );
             let msg_id = MsgId::new(arg1.parse()?);
-            context
-                .send_webxdc_status_update(msg_id, arg2, "this is a webxdc status update")
-                .await?;
+            context.send_webxdc_status_update(msg_id, arg2).await?;
         }
         "videochat" => {
             ensure!(sel_chat.is_some(), "No chat selected.");