patch 8.0.1333: some tests are run twice

Problem:    Some tests are run twice.
Solution:   Invoked most utf8 tests only from test_alot_utf8. (Yegappan
            Lakshmanan, closes #2369)
diff --git a/src/testdir/test_mksession_utf8.vim b/src/testdir/test_mksession_utf8.vim
index c05a1d3..8ffbba2 100644
--- a/src/testdir/test_mksession_utf8.vim
+++ b/src/testdir/test_mksession_utf8.vim
@@ -99,6 +99,7 @@
   call delete('test_mks.out')
   call delete(tmpfile)
   let &wrap = wrap_save
+  set sessionoptions& splitbelow& fileencoding&
 endfunc
 
 " vim: shiftwidth=2 sts=2 expandtab