Remove deprecated config checker and make <die> actually useful.

Remove deprecated config checker and make <die> actually useful.

- Remove the deprecated config tag checker. This checker is neither
  exhaustive nor is it particularly accurate. Instead the new docs
  site will contain a page detailing the breaking changes between
  releases.
- Remove the insulting <die> tags in inspircd.conf.example and add
  some descriptive ones in files that it is critical for the user
  to edit correctly.
- Show the message from the <die> tag so the user actually knows
  what they did wrong.