Prefer LightRenderer on Windows if it's available

Fix #1766

src/tui/dummy.go

@@ -6,10 +6,6 @@ package tui
 
 type Attr int
 
-func HasFullscreenRenderer() bool {
-	return false
-}
-
 func (a Attr) Merge(b Attr) Attr {
 	return a | b
 }

src/tui/tcell.go

@@ -15,10 +15,6 @@ import (
 	"github.com/mattn/go-runewidth"
 )
 
-func HasFullscreenRenderer() bool {
-	return true
-}
-
 func (p ColorPair) style() tcell.Style {
 	style := tcell.StyleDefault
 	return style.Foreground(tcell.Color(p.Fg())).Background(tcell.Color(p.Bg()))