lint: Convert stylecheck exclude to configuration

By default, stylecheck checks for missing package comments. Given that we don't really use these, this of course generates a lot of linting violations for us. Because of this, we have added an exclude rule to just skip over those violations completely. Excludes aren't the correct way to go about this, though: the stylecheck linter can be configured to skip specific checks, which is what we should be doing instead.

Convert the exclude rule to stylecheck configuration.