textproc/py-transifex-client: Mark DEPRECATED

Transifex is retiring the v2 API and has introduced a new go-based
client for v3 API. adridg@ has ported the new client which is available
at textproc/go-transifex-client.

The v2 API application doesn't work anymore (april 2023), the API it
wants to talk to seems to be dead or moved to app.transifex.com.

PR: 271050
Reported by: adridg