patch 8.1.0811: too many #ifdefs

Problem:    Too many #ifdefs.
Solution:   Graduate FEAT_MBYTE, the final chapter.
diff --git a/src/testdir/runtest.vim b/src/testdir/runtest.vim
index a8b43aa..3f49ccb 100644
--- a/src/testdir/runtest.vim
+++ b/src/testdir/runtest.vim
@@ -49,13 +49,9 @@
 " This also enables use of line continuation.
 set nocp viminfo+=nviminfo
 
-" Use utf-8 or latin1 by default, instead of whatever the system default
-" happens to be.  Individual tests can overrule this at the top of the file.
-if has('multi_byte')
-  set encoding=utf-8
-else
-  set encoding=latin1
-endif
+" Use utf-8 by default, instead of whatever the system default happens to be.
+" Individual tests can overrule this at the top of the file.
+set encoding=utf-8
 
 " REDIR_TEST_TO_NULL has a very permissive SwapExists autocommand which is for
 " the test_name.vim file itself. Replace it here with a more restrictive one,