Remove outdated palette button hiding code

[marcustyphoon]

User-facing changes

• None, mostly.

Technical explanation

The code in question, used to hide the nonfunctional-with-this-extension "change palette" button in the UI:

• Doesn't work, as the capitalization of its selector is wrong (at some point I guess it changed to Change palette)
• Isn't needed, as this button doesn't exist in the current version of the UI. I don't know of any currently updated scripts that revert the UI in a way that brings back the code path that produces the button in question, either, though the code remains.
• Logs an error in the dashboard occasionally (I did not look into reproducing this reliably, due to the previous bullet points).

Therefore, this removes it.

Issues this closes

n/a