Revert "Prefer LightRenderer on Windows if it's available"

This reverts commit 7915e365b3
due to https://github.com/junegunn/fzf.vim/issues/1152#issuecomment-719696495.

src/tui/dummy.go

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

src/tui/tcell.go

@@ -15,6 +15,10 @@ 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()))