cmd/go: revert "add graphviz output to graph command"

This reverts commit 723479bc.

Reason for revert: other tools should convert the graph output to graphviz.

Change-Id: Ide5b8f0b061aaff74bb6ba4c2a8f8768d1fbc05a
Reviewed-on: https://go-review.googlesource.com/130295Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/go/internal/modcmd/graph.go

@@ -18,25 +18,15 @@ import (
 )
 
 var cmdGraph = &base.Command{
-	UsageLine: "go mod graph [-dot]",
+	UsageLine: "go mod graph",
 	Short:     "print module requirement graph",
 	Long: `
 Graph prints the module requirement graph (with replacements applied)
 in text form. Each line in the output has two space-separated fields: a module
 and one of its requirements. Each module is identified as a string of the form
 path@version, except for the main module, which has no @version suffix.
-
-The -dot flag generates the output in graphviz format that can be used
-with a tool like dot to visually render the dependency graph.
 	`,
-}
-
-var (
-	graphDot = cmdGraph.Flag.Bool("dot", false, "")
-)
-
-func init() {
-	cmdGraph.Run = runGraph // break init cycle
+	Run: runGraph,
 }
 
 func runGraph(cmd *base.Command, args []string) {
@@ -61,21 +51,10 @@ func runGraph(cmd *base.Command, args []string) {
 	work.Add(modload.Target)
 	work.Do(1, func(item interface{}) {
 		m := item.(module.Version)
-		if *graphDot {
-			if m.Version == "" {
-				out = append(out, "\""+m.Path+"\" [label=<"+m.Path+">]\n")
-			} else {
-				out = append(out, "\""+m.Path+"\" [label=<"+m.Path+"<br/><font point-size=\"9\">"+m.Version+"</font>>]\n")
-			}
-		}
 		list, _ := reqs.Required(m)
 		for _, r := range list {
 			work.Add(r)
-			if *graphDot {
-				out = append(out, "\""+m.Path+"\" -> \""+r.Path+"\"\n")
-			} else {
-				out = append(out, format(m)+" "+format(r)+"\n")
-			}
+			out = append(out, format(m)+" "+format(r)+"\n")
 		}
 		if m == modload.Target {
 			deps = len(out)
@@ -87,14 +66,8 @@ func runGraph(cmd *base.Command, args []string) {
 	})
 
 	w := bufio.NewWriter(os.Stdout)
-	if *graphDot {
-		w.WriteString("digraph deps {\nrankdir=LR\n")
-	}
 	for _, line := range out {
 		w.WriteString(line)
 	}
-	if *graphDot {
-		w.WriteString("}\n")
-	}
 	w.Flush()
 }