Xpra: Ticket #2344: don't load codecs we don't need

Related to #2341, #1838, #1861.

When we specify --encodings=rgb, there is no need to load the jpeg or webp picture codecs. (or even python-pillow, though that one will get loaded no matter what)

Sat, 29 Jun 2019 20:36:01 GMT - Antoine Martin: status changed; resolution set

Done in r23045.

Sat, 23 Jan 2021 05:48:47 GMT - migration script:

this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/2344