all: fix printf(var) mistakes detected by latest printf checker

The CodeWriter.WriteComment method is odd. It calls fmt.Sprintf
on its arguments so the caller doesn't need to, but isn't named
something like WriteCommentf as I'd expect. I tried renaming it,
but it became a bigger change than I wanted. Leaving that for a
future CL - this one just fixes clear mistakes to fix the build.

For golang/go#69267.

Change-Id: Ifba42d4512696194fbf21d6c8d3da76440b1ce9e
Reviewed-on: https://go-review.googlesource.com/c/text/+/610676
Reviewed-by: Tim King <taking@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

collate/build/builder_test.go

@@ -65,7 +65,7 @@ func newBuilder(t *testing.T, ducet []ducetElem) *Builder {
 			ces = append(ces, ce.w)
 		}
 		if err := b.Add([]rune(e.str), ces, nil); err != nil {
-			t.Errorf(err.Error())
+			t.Error(err)
 		}
 	}
 	b.t = &table{}

collate/build/trie_test.go

@@ -29,7 +29,7 @@ func makeTestTrie(t *testing.T) trie {
 	idx.addTrie(n)
 	tr, err := idx.generate()
 	if err != nil {
-		t.Errorf(err.Error())
+		t.Error(err)
 	}
 	return *tr
 }

internal/cldrtree/generate.go

@@ -21,7 +21,7 @@ func generate(b *Builder, t *Tree, w *gen.CodeWriter) error {
 
 	fmt.Fprintf(w, "var tree = &cldrtree.Tree{locales, indices, buckets}\n\n")
 
-	w.WriteComment("Path values:\n" + b.stats())
+	w.WriteComment("Path values:\n%s", b.stats())
 	fmt.Fprintln(w)
 
 	// Generate enum types.

internal/gen/code.go

@@ -342,8 +342,7 @@ func (w *CodeWriter) writeSlice(x interface{}, isArray bool) {
 			if !reflect.DeepEqual(zero, x) {
 				line := fmt.Sprintf("%#v,\n", x)
 				line = line[strings.IndexByte(line, '{'):]
-				w.printf("%d: ", i)
-				w.printf(line)
+				w.printf("%d: %s", i, line)
 			}
 		}
 	case reflect.Array: