Enable `nolintlint` linter

There currently exists a pattern of `//nolint` directives disabling linters without saying why.
We should enable the `nolintlint` linter, that'll require explanatory comments for `//nolint` directives.
This helps the reader understand why a `//nolint` directive was appropriate.
As a bonus, it'll also automatically remove //nolint directives that don't do anything anymore.