Remove terminal.Writer

terminal.Writer is now just a wrapper around stdio.Stdout() without
any useful functionality.  Replace it with stdio.Stdout() as an
io.Writer.

Test: ui/terminal/status_test.go
Change-Id: I5bc5476afdca950b505642f0135a3af9d37fbe24
diff --git a/ui/terminal/smart_status.go b/ui/terminal/smart_status.go
index 5edc21a..a52fdc2 100644
--- a/ui/terminal/smart_status.go
+++ b/ui/terminal/smart_status.go
@@ -16,6 +16,7 @@
 
 import (
 	"fmt"
+	"io"
 	"strings"
 	"sync"
 
@@ -23,7 +24,7 @@
 )
 
 type smartStatusOutput struct {
-	writer    Writer
+	writer    io.Writer
 	formatter formatter
 
 	lock sync.Mutex
@@ -34,7 +35,7 @@
 // NewSmartStatusOutput returns a StatusOutput that represents the
 // current build status similarly to Ninja's built-in terminal
 // output.
-func NewSmartStatusOutput(w Writer, formatter formatter) status.StatusOutput {
+func NewSmartStatusOutput(w io.Writer, formatter formatter) status.StatusOutput {
 	return &smartStatusOutput{
 		writer:    w,
 		formatter: formatter,
@@ -133,7 +134,7 @@
 	// Run this on every line in case the window has been resized while
 	// we're printing. This could be optimized to only re-run when we get
 	// SIGWINCH if it ever becomes too time consuming.
-	if max, ok := s.writer.termWidth(); ok {
+	if max, ok := termWidth(s.writer); ok {
 		if len(str) > max {
 			// TODO: Just do a max. Ninja elides the middle, but that's
 			// more complicated and these lines aren't that important.