feat: remove extra rules added to match browserslist best practices

[brian-smith-tcril]

See #16 (comment)

[brian-smith-tcril]

Bringing over today's slack conversation about this:

@adamstankiewicz: [clarification] Isn't it expected that expanding the browserslist support would start including polyfills/shims that weren't there before, for supporting additional browsers it previously didn't need to support?
Are we sure those "unnecessary backwards compatibility shims" aren't expected due to the updated config?

@brian-smith-tcril: It is expected, I think the question is if it's desired

@bradenmacdonald: Some new shims and/or CSS adaptions etc were expected but the extent surprised me. I didn't realize the expanded support would include such old targets that required essentially everything to be shimmed. In the icon files for example, there's more shims than code in each file. I don't think it's worth it, especially since we didn't have any actual reports/complaints of incompatibility that we're trying to solve.

[arbrandes]

Yeah, let's ditch the best practices. The cost is clearly not worth it.

[bradenmacdonald]

Sorry for the churn here :p