golangci-lint: remove "strict" checking

The corresponding "pull-kubernetes-verify-lint" job was already removed
earlier. Manual strict checking was still possible, but doesn't really make
sense for the same reasons why the job was removed (e.g. the decisions which
checks should be "strict" were too arbitrary).

The explanations for "hints" no longer end with "In general please prefer to
fix the error, ..." because that was misleading and only really applied to the
checks for existing code. For those checks we prefer to fix errors instead of
suppressing them, but not for hints.

hack/update-golangci-lint-config.sh

@@ -40,5 +40,4 @@ generate () {
 
 # Regenerate.
 generate hack/golangci.yaml Base=1
-generate hack/golangci-strict.yaml Strict=1
 generate hack/golangci-hints.yaml Hints=1