enable full linter across the codebase (#9620)

enable linter using golangci-lint across
codebase to run a bunch of linters together,
we shall enable new linters as we fix more
things the codebase.

This PR fixes the first stage of this
cleanup.

pkg/s3select/sql/value_test.go

@@ -160,9 +160,6 @@ func TestValue_Equals(t *testing.T) {
 }
 
 func TestValue_CSVString(t *testing.T) {
-	type fields struct {
-		value interface{}
-	}
 	type test struct {
 		name    string
 		want    string