ui: prune unneeded dependencies

[couchand]

Every byte of dependency counts against us twice: it bloats our binary size in addition to the usual concerns about bandwidth to the client & parse-execute time. We should make sure every dependency we include is necessary (and then make the admin UI load as quick as possible, see #18668). NVD3 is our second-biggest dependency, and we already have an issue to eliminate that - #18620. Let's evaluate the rest of our dependencies and make sure they all add enough value to justify including.

[couchand]

In particular, it looks like a number of our dev dependencies are getting pulled into the bundle (I noticed chai, css-loader, and some typings). After #18349 lands, we should check again to see if we can update the webpack config to prevent this.

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