feat: Deduplicate in more places (#6464)

Deduplicate:
- In the REPL
- In `store_from_base64()`, which writes avatars received in headers
- In a few tests
- The saved messages, broadcast, device, archive icons
- The autocrypt setup message

1-2 more PRs, and we can get rid of `BlobObject::create`,
`sanitise_name()`, and some others

src/contact.rs

@@ -345,7 +345,7 @@ async fn import_vcard_contact(context: &Context, contact: &VcardContact) -> Resu
         return Ok(id);
     }
     let path = match &contact.profile_image {
-        Some(image) => match BlobObject::store_from_base64(context, image, "avatar").await {
+        Some(image) => match BlobObject::store_from_base64(context, image) {
             Err(e) => {
                 warn!(
                     context,