Revert "[workspace] Upgrade usockets and uwebsockets"

[jwnimmer-tri]

Reverts #18259. Re-opens #17910.

We have some evidence that a Docker image using this commit will not work with the Nginx proxy server we use for our Deepnote tutorials, yielding a "Bad Gateway" error message instead.

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This change is 

[jwnimmer-tri]

rubber stamp on pure revert.

Given the intricacies of testing this problem, it's a bit difficult to know for sure that this is the offending commit but anyway reverting it is no great loss. The purpose of the upgrade was to suss out problems with upstream versions earlier rather than later, which it seems like this has accomplished.

We'll re-use #17910 to track the upgrade (and possible incompatibility).

[RussTedrake]

also. thanks!!

[RussTedrake]

Since this problem just surfaced again, due to #18516, let me describe here an acceptance test:

Using the drake tutorials on Deepnote, running the first two cells of the authoring_multibody_plant tutorial should allow you to then click on the url and open a meshcat instance. When usockets/uwebsockets was upgraded, we could not connect to meschat, and instead see a 502 Bad Gateway error message from ngix.