ci: Remove references to archived altair_viewer and altair_saver in ci, docs, and tests. Uninstall anywidget and vl-convert-python during one test run

[binste]

Now that both altair_viewer and altair_saver are archived and not compatible with Altair anyway, I'd suggest to remove all references to them to clean up the code base a bit. In this PR, I:

• removed all references to altair_viewer
• removed all references to altair_saver except for 1 mention in the docs
• uninstall anywidget and vl-convert-python as well in the build workflow to make sure we don't introduce hard dependencies. This is not directly related to the rest of the PR but hope it's ok for efficiency reasons. Else, happy to take it out!
• added a deprecation warning if someone uses the webdriver argument to the .save method as it's not relevant for vl-convert. I didn't want to remove it just now as users might still have it set although they have switched to vl-convert in which case it has just been ignored so far
• run test_save_html again with inline=True as vl-convert supports it

[binste]

Need to wait for #3418 to be resolved before tests can run.

[jonmmease]

Looks great. Thanks for doing this cleanup @binste!

[mattijn]

#3418 is resolved, but tests are not yet happy. It now raises an anywidget dependency issue, see https://github.com/vega/altair/actions/runs/9090334764/job/24983082085. Probably related to this sentence in OP:

uninstall anywidget and vl-convert-python as well in the build workflow to make sure we don't introduce hard dependencies.

Can you have a look to this @binste. Thanks!

[binste]

Thank you both! I added pytest.skip statements to some more tests which relied on vl-convert or anywidget. Now, the tests can be run with only Altair's required dependencies. Any tests which require optional dependencies are skipped. Merging as it's only CI changes and Jon approved an earlier version but happy to do work in a follow-up PR if anyone has comments.