If PDF.js is on, show PDF.js. Remove logic to fall back to UV if split works are present

[ShanaLMoore]

Summary

There are issues with the special logic applied to fall back to the UV even with PDF.js is on, which occurs for specific conditions (ie: split works exist). Per Katharine, for now let's remove that logic and always show PDF.js when that feature flag is on.

https://assaydepot.slack.com/archives/C0313NJV9PE/p1733411068582639

Acceptance Criteria

• Regardless of the conditionals, when PDF.js is enabled it should the display PDF.js viewer.

Screenshots or Video

Testing Instructions

To be filled out by dev

Notes

[KatharineV]

Just dropping in a note here. The existing logic is preferred, if the UV can be fixed so it will display split works as it did before the cutover. The existing logic is ideal when both viewers are functional. If it is possible to fix both the UV and PDF.js so they function as they did before Valkyrie and Version 6, then we would be thrilled.

Removing the logic and relying on just PDF.js is a last resort option that we choose simply to prioritize showing works throughout the repo.

Question: What will happen to non-PDF works if we remove the logic and rely on PDF.js? Will TIFF and JPEG works render in the viewer? Will embedded videos still display?

Thanks for answering that question and considering other paths before reverting the logic.