Remove multi-context restrictions for publishing image sequences on farm

[antirotor]

Changelog Description

Removing assert that context data must be same as instance data will allow publishing image data to different context in one go.
That sanity check was there because we didn't support publishing to different context before (like multishot workflow), but this should be possible now.

⚰️ This is also removing support for multiple jsons files as it was just complicating the code and it wasn't used anywhere.

Additional info

More work on different DCCs needs to be done to seamlessly support multishot workflow - like Maya restrict only one rendering instance, Nuke enforce unique instance name (so you can't publish renderMain to multiple shots), etc.

Testing notes:

1. Open Nuke
2. Create 3 write instances (you need to change variant name to make them unique).
3. Direct them in the Publisher to different shots.
4. Render and publish on farm.

Note

This is ayon-core version of ynput/OpenPype#6088

[cuID:AY-1003]

[tokejepsen]

Tested successfully in Nuke 15.