patch 8.1.0811: too many #ifdefs

Problem:    Too many #ifdefs.
Solution:   Graduate FEAT_MBYTE, the final chapter.
diff --git a/src/testdir/test_writefile.vim b/src/testdir/test_writefile.vim
index d1f6346..2e47b48 100644
--- a/src/testdir/test_writefile.vim
+++ b/src/testdir/test_writefile.vim
@@ -33,7 +33,7 @@
 endfunc
 
 func Test_writefile_fails_conversion()
-  if !has('multi_byte') || !has('iconv') || system('uname -s') =~ 'SunOS'
+  if !has('iconv') || system('uname -s') =~ 'SunOS'
     return
   endif
   set nobackup nowritebackup