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

ui/build/context.go

@@ -16,12 +16,12 @@ package build
 
 import (
 	"context"
+	"io"
 
 	"android/soong/ui/logger"
 	"android/soong/ui/metrics"
 	"android/soong/ui/metrics/metrics_proto"
 	"android/soong/ui/status"
-	"android/soong/ui/terminal"
 	"android/soong/ui/tracer"
 )
 
@@ -35,7 +35,7 @@ type ContextImpl struct {
 
 	Metrics *metrics.Metrics
 
-	Writer terminal.Writer
+	Writer io.Writer
 	Status *status.Status
 
 	Thread tracer.Thread