Remove nerdtree.

I don't use it.  I don't agree with the idea of file explorer in Vim.

Signed-off-by: Anurag Priyam <anurag08priyam@gmail.com>
Save viminfo to ~/.vim.

So it can be easily synced via Google Drive or Dropbox.

Signed-off-by: Anurag Priyam <anurag08priyam@gmail.com>