vim-patch:8.1.0811: too many #ifdefs

Problem:    Too many #ifdefs.
Solution:   Graduate FEAT_MBYTE, the final chapter.
30276f2beb

src/nvim/testdir/test_regex_char_classes.vim

@@ -1,9 +1,6 @@
 " Tests for regexp with backslash and other special characters inside []
 " Also test backslash for hex/octal numbered character.
 "
-if !has('multi_byte')
-  finish
-endif
 
 scriptencoding utf-8