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
 }