Do not enable delayed expansion mode when running cmd.exe

And simplify the argument escaping code. Fix #3764.

This may breaks some existing use cases, but the mode causes too much
trouble when escaping arguments and it makes some things not possible.

  # Now you can pass special characters to rg process without any escaping problems: &|<>()@^%!
  fzf --ansi --disabled --bind "change:reload:rg --column --line-number --no-heading --color=always --smart-case -- {q}"

  # No sudden expansion of the arguments on '!'
  fzf --disabled --preview "echo {q} {n} {}" --query "&|<>()@^%!" --prompt "&|<>()@^%!"

plugin/fzf.vim

@@ -59,12 +59,9 @@ if s:is_win
     return iconv(a:str, &encoding, 'cp'.s:codepage)
   endfunction
   function! s:wrap_cmds(cmds)
-    return map([
-      \ '@echo off',
-      \ 'setlocal enabledelayedexpansion']
+    return map(['@echo off']
     \ + (has('gui_running') ? ['set TERM= > nul'] : [])
-    \ + (type(a:cmds) == type([]) ? a:cmds : [a:cmds])
-    \ + ['endlocal'],
+    \ + (type(a:cmds) == type([]) ? a:cmds : [a:cmds]),
     \ '<SID>enc_to_cp(v:val."\r")')
   endfunction
 else
@@ -83,8 +80,6 @@ else
   endfunction
 endif
 
-let s:cmd_control_chars = ['&', '|', '<', '>', '(', ')', '@', '^', '!']
-
 function! s:shellesc_cmd(arg)
   let e = '"'
   let slashes = 0
@@ -94,10 +89,6 @@ function! s:shellesc_cmd(arg)
     elseif c ==# '"'
       let e .= repeat('\', slashes + 1)
       let slashes = 0
-    elseif c ==# '%'
-      let e .= '%'
-    elseif index(s:cmd_control_chars, c) >= 0
-      let e .= '^'
     else
       let slashes = 0
     endif