chore: remove unused internal yaml2json command

The string "yaml2json" doesn't occur anywhere outside of this package.

internal/yaml2json/main.go

@@ -1,26 +0,0 @@
-package main
-
-import (
-	"io/ioutil"
-	"log"
-	"os"
-
-	yaml "github.com/ghodss/yaml"
-)
-
-// yaml2json reads yaml data from stdin and outputs json to stdout.
-// There are no arguments or flags.
-func main() {
-	in, err := ioutil.ReadAll(os.Stdin)
-	if err != nil {
-		log.Fatal(err)
-	}
-	out, err := yaml.YAMLToJSON(in)
-	if err != nil {
-		log.Fatal(err)
-	}
-	_, err = os.Stdout.Write(out)
-	if err != nil {
-		log.Fatal(err)
-	}
-}