remove now useless option g:startify_unlisted_buffer

doc/startify.txt

@@ -177,15 +177,6 @@ Best practices:
 - (you might want to keep 'j' and 'k' for navigation)
 
 
-============-
-
-    let g:startify_unlisted_buffer = 1
-
-Some bad plugins like minibufexpl break, when there is no listed buffer.
-People can set this variable to 0, to work around that. As a consequence the
-start screen buffer won't be removed, even after triggering an action from the
-start screen.
-
 ============-
 
     let g:startify_enable_special = 1

plugin/startify.vim

@@ -46,9 +46,6 @@ function! s:insane_in_the_membrane() abort
   if (v:version >= 703)
     setlocal norelativenumber
   endif
-  if get(g:, 'startify_unlisted_buffer', 1)
-    setlocal nobuflisted
-  endif
   setfiletype startify
 
   let special = get(g:, 'startify_enable_special', 1)