Revert "Make :Plug command unavailable after end()"

This reverts commit d369322e03f805c6f7b64a9c51fb5f0dac8c8bcb.

plug.vim

@@ -76,21 +76,17 @@ function! plug#begin(...)
   let g:plug_home = home
   let g:plugs = {}
 
-  silent! delcommand PlugInstall
-  silent! delcommand PlugUpdate
-  silent! delcommand PlugClean
-  silent! delcommand PlugUpgrade
-  silent! delcommand PlugStatus
-  command! -nargs=+ Plug call s:add(1, <args>)
+  command! -nargs=+ Plug        call s:add(1, <args>)
+  command! -nargs=* PlugInstall call s:install(<f-args>)
+  command! -nargs=* PlugUpdate  call s:update(<f-args>)
+  command! -nargs=0 -bang PlugClean call s:clean('<bang>' == '!')
+  command! -nargs=0 PlugUpgrade if s:upgrade() | execute "source ". s:me | endif
+  command! -nargs=0 PlugStatus  call s:status()
 
   return 1
 endfunction
 
 function! plug#end()
-  if !exists(':Plug')
-    return
-  endif
-
   let keys = keys(g:plugs)
   while !empty(keys)
     let keys = keys(s:extend(keys))
@@ -105,14 +101,6 @@ function! plug#end()
       execute "set rtp+=".rtp.'after'
     endif
   endfor
-
-  delcommand Plug
-  command! -nargs=* PlugInstall call s:install(<f-args>)
-  command! -nargs=* PlugUpdate  call s:update(<f-args>)
-  command! -nargs=0 -bang PlugClean call s:clean('<bang>' == '!')
-  command! -nargs=0 PlugUpgrade if s:upgrade() | execute "source ". s:me | endif
-  command! -nargs=0 PlugStatus  call s:status()
-
   filetype plugin indent on
   syntax on
 endfunction