vim-patch:8.1.1756: autocommand that splits window messes up window layout

Problem:    Autocommand that splits window messes up window layout.
Solution:   Disallow splitting a window while closing one.  In ":all" give an
            error when moving a window will not work.
1417c766f5

Expected error number was changed to E242 in Vim in patch 8.2.1183, and
patch 8.2.2420 (which has already been ported) made the test no longer
throw E249 in Vim, so just use E242 in the test.

test/functional/autocmd/autocmd_spec.lua

@@ -548,18 +548,6 @@ describe('autocmd', function()
       neq({}, meths.get_autocmds { group = "filetypedetect" })
     end)
 
-    it('should not access freed mem', function()
-      source [[
-        au BufEnter,BufLeave,WinEnter,WinLeave 0 vs xxx
-        arg 0
-        argadd
-        all
-        all
-        au!
-        bwipe xxx
-      ]]
-    end)
-
     it('should allow comma-separated patterns', function()
       source [[
         augroup TestingPatterns