Revert "Steal Windows shell escaping from dispatch.vim"

This reverts commit 15450eff27.

autoload/nrepl/fireplace_connection.vim

@@ -34,14 +34,7 @@ function! s:shellesc(arg) abort
   if a:arg =~ '^[A-Za-z0-9_/.-]\+$'
     return a:arg
   elseif &shell =~# 'cmd'
-    if &shellxquote ==# '"'
-      return '"' . substitute(a:arg, '"', '""', 'g') . '"'
-    else
-      let esc = exists('+shellxescape') ? &shellxescape : '"&|<>()@^'
-      return &shellxquote .
-            \ substitute(a:arg, '['.esc.']', '^&', 'g') .
-            \ get({'(': ')', '"(': ')"'}, &shellxquote, &shellxquote)
-    endif
+    return '"'.substitute(substitute(a:arg, '"', '""""', 'g'), '%', '"%"', 'g').'"'
   else
     let escaped = shellescape(a:arg)
     if &shell =~# 'sh' && &shell !~# 'csh'