Audit all ESLint config for performance issues

We've found this ESLint configuration to be very slow, and we suspect it's in part due to redundant or unnecessary rules.

We should audit all of our rules to ensure that none of them are redundant or unnecessary, with particular attention paid to any that have a substantial performance impact.

This should be done after `prettier` has been added to our base config (#91), as many of the performance issues are related to `prettier` usage.