Replace custom ESLint warning tracking with bulk suppressions

[mcmire]

A recent version of ESLint introduced the bulk suppressions feature, which allows you to suppress certain rules by passing --suppress-rule when calling eslint on the command line. Instances of suppressed rules are captured in a file similar to eslint-suppressions.json, and extra violations past the numbers recorded here are reported. This is very similar to the custom ESLint script we wrote a while back and would allow us to replace it entirely. This would also allow us to keep all violations at the error level instead of introducing a warning level, making yarn lint:fix work again.