compose: Delete drafts with attachments.

Draft messages containing attachments, polls, or other items that cannot be locally 
echoed would not be deleted after sending the message. 

The explanation is simple: We only cleared the draft associated with a message in the 
`reify_message_id` local echo code path.

Fixes zulip#24063.

static/js/compose.js

@@ -203,6 +203,9 @@ export function clear_compose_box() {
 
 export function send_message_success(local_id, message_id, locally_echoed) {
     if (!locally_echoed) {
+        if ($("#compose-textarea").data("draft-id")) {
+            drafts.draft_model.deleteDraft($("#compose-textarea").data("draft-id"));
+        }
         clear_compose_box();
     }