markdown: Treat more twitter codes as also permanent failures.
markdown: Treat more twitter codes as also permanent failures.

Per the API documentation[1], the following codes all correspond to
HTTP 404:

 - `34`: **Sorry, that page does not exist.**  The specified resource
   was not found.
 - `144`: **No status found with that ID.**  The requested Tweet ID is
   not found (if it existed, it was probably deleted)
 - `421`: **This Tweet is no longer available.**  The Tweet cannot be
   retrieved. This may be for a number of reasons.
 - `422`: **This Tweet is no longer available because it violated the
   Twitter Rules.**  The Tweet is not available in the API.

Treat all of these identically.

[1] https://developer.twitter.com/en/docs/basics/response-codes

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