When Telegram flood control triggers 3+ consecutive edit failures, the
stream consumer enters fallback mode and sends the complete response as
a new message. This leaves the user seeing two messages: a frozen
partial (with cursor) and the full duplicate.
After the fallback chunks are sent successfully, delete the original
partial message so the user only sees one complete response. The delete
is best-effort — if it fails (e.g. flood still active, missing
permissions), the full answer is still delivered.
Fixes#16668
4eb8479ebd