Remove web-mode customization

- Code indent offset is subjected to personal taste, I think we should
  stick to the web-mode default, which is sensible enough, and leave it
  to the user to decide.
- `web-mode-disable-autocompletion` is no longer used by web-mode.
- As to `newline-and-indent`, I think we should be consistent across all
  major modes. And this line of code will become useless with Emacs 24.4.
Make web-mode play nice with smartparens

web-mode's auto paring is in conflict with smartparens. With
smartparens, since the closing '>' is inserted right after the opening
'<' and web-mode is not aware of that, the extra closing '>' would be
inserted. That's very annoying.
Merge pull request #572 from toctan/prelude-web

Make web-mode play nice with smartparens