golangci: Drop strict linting rules

Back in ce3f2ee4 (Lint: split up "make lint" and "make lint-strict" configs, 2021-01-19), we have split up our linting rules into a "normal" set which needs to be satisfied for each CI run and a "strict" set which only runs on scheduled pipelines. I highly doubt that anybody ever takes a look at the strict linter job: there are no MRs which clean up any of its additional violations.

Let's remove this job and be done with it. Anybody wishing to fix up linting rules can just play with our normal linting rules and is unlikely to use CI for this anyway.