tests: Migrate legacy test 8. #4179

The test produces some "hit enter" prompts and error messages that had to be
dealt with by `feed`ing CTRL-L to nvim.

src/nvim/testdir/Makefile

@@ -8,7 +8,6 @@ VIMPROG := ../../../build/bin/nvim
 SCRIPTSOURCE := ../../../runtime
 
 SCRIPTS := \
-           test8.out              \
            test13.out             \
            test14.out             \
            test17.out             \

src/nvim/testdir/test8.in

@@ -1,43 +0,0 @@
-Test for BufWritePre autocommand that deletes or unloads the buffer.
-Test for BufUnload autocommand that unloads all other buffers.
-
-STARTTEST
-:au BufWritePre Xxx1 bunload
-:au BufWritePre Xxx2 bwipe
-/^start of
-A1:.,/end of/w! Xxx1  " write test file Xxx1
-$r2:.,/end of/w! Xxx2   " write test file Xxx2
-:e! Xxx2                " edit Xxx2
-:bdel test8.in		" delete this file from the buffer list
-:e Xxx1                 " edit Xxx1
-:w                      " write it, will unload it and give an error msg
-:w! test.out            " Write contents of this file
-:e! Xxx2                " start editing Xxx2
-:bwipe test.out         " remove test.out from the buffer list
-:w                      " write it, will delete the buffer and give an error msg
-:w >>test.out           " Append contents of this file
-:au! BufWritePre
-:func CloseAll()
-  let i = 0
-  while i <= bufnr('$')
-    if i != bufnr('%') && bufloaded(i)
-      exe  i . "bunload"
-    endif
-    let i += 1
-  endwhile
-endfunc
-:func WriteToOut()
-  edit! test.out
-  $put ='VimLeave done'
-  write
-endfunc
-:set shada='100
-:au BufUnload * call CloseAll()
-:au VimLeave * call WriteToOut()
-:q
-:qa!
-ENDTEST
-
-start of Xxx
-	test
-end of Xxx

src/nvim/testdir/test8.ok

@@ -1,7 +0,0 @@
-start of Xxx2
-	test
-end of Xxx
-start of Xxx1
-	test
-end of Xxx
-VimLeave done