Remove dead code

Close #1194

plug.vim

@@ -238,7 +238,6 @@ endfunction
 
 function! plug#begin(...)
   if a:0 > 0
-    let s:plug_home_org = a:1
     let home = s:path(s:plug_fnamemodify(s:plug_expand(a:1), ':p'))
   elseif exists('g:plug_home')
     let home = s:path(g:plug_home)