move ASM strings to core, point to "Add Second Device" (#6777)

this PR moves now advanced/unsupported ASM strings to core, removing
work from translations, esp. as another hint is added which would
require retranslations. it is better to have that just in english, it is
a nerd feature anyways.

moverover, this PR removes special rendering of ASM in the summary,
which might be confusion, but mainly it is now unneeded, dead code

i'll do another android PR that will point to "Add Second Device"
already on ASM generation EDIT: done at
https://github.com/deltachat/deltachat-android/pull/3726

targets https://github.com/deltachat/deltachat-desktop/issues/4946

src/mimefactory.rs

@@ -16,6 +16,7 @@ use tokio::fs;
 use crate::blob::BlobObject;
 use crate::chat::{self, Chat};
 use crate::config::Config;
+use crate::constants::ASM_SUBJECT;
 use crate::constants::{Chattype, DC_FROM_HANDSHAKE};
 use crate::contact::{Contact, ContactId, Origin};
 use crate::context::Context;
@@ -1303,7 +1304,7 @@ impl MimeFactory {
                     mail_builder::headers::raw::Raw::new("v1").into(),
                 ));
 
-                placeholdertext = Some(stock_str::ac_setup_msg_body(context).await);
+                placeholdertext = Some(ASM_SUBJECT.to_string());
             }
             SystemMessage::SecurejoinMessage => {
                 let step = msg.param.get(Param::Arg).unwrap_or_default();