Remove nerdtree settings from core to nerdtree plug

vim/.config/vim/plug.d/core.vim

@@ -1,28 +1,5 @@
 Plug 'editorconfig/editorconfig-vim', { 'tag': 'v1.1.1' }
 Plug 'tpope/vim-surround'
-
-" UltiSnips
 Plug 'SirVer/ultisnips', { 'tag': '3.2' }
-let g:UltiSnipsSnippetDirectories = [ 'UltiSnips', 'snips' ]
-
-" NerdTree
-Plug 'preservim/nerdtree', { 'on':  'NERDTreeToggle', 'tag': '6.9.8' }
 
-" Close all open buffers on entering a window if the only
-" buffer that's left is the NERDTree buffer
-function! s:CloseIfOnlyNerdTreeLeft()
-    if exists("t:NERDTreeBufName")
-        if bufwinnr(t:NERDTreeBufName) != -1
-            if winnr("$") == 1
-                q
-            endif
-        endif
-    endif
-endfunction
-
-let g:NERDTreeDirArrowExpandable = '▸'
-let g:NERDTreeDirArrowCollapsible = '▾'
-let NERDTreeDirArrows = 1
-let NERDTreeIgnore = [ '\.pyc$', '\.swp$' ]
-
-autocmd WinEnter * call s:CloseIfOnlyNerdTreeLeft()
+let g:UltiSnipsSnippetDirectories = [ 'UltiSnips', 'snips' ]