patch 8.1.0811: too many #ifdefs

Problem:    Too many #ifdefs.
Solution:   Graduate FEAT_MBYTE, the final chapter.
diff --git a/src/testdir/test_display.vim b/src/testdir/test_display.vim
index e0e3e3b..81ffb2c 100644
--- a/src/testdir/test_display.vim
+++ b/src/testdir/test_display.vim
@@ -39,7 +39,7 @@
 endfunc
 
 func Test_display_foldtext_mbyte()
-  if !has("folding") || !has("multi_byte")
+  if !has("folding")
     return
   endif
   call NewWindow(10, 40)