Inline Manual::WithdrawService#manual
Inline Manual::WithdrawService#manual

Inlining these methods should make it easier to see the behaviour of the
`#call` method.

Note that the `rescue KeyError` statement is redundant as `Manual.find`
raises a `Manual::NotFoundError` and not a `KeyError`.

alphagov/manuals-publisher,alphagov/manuals-publisher,alphagov/manuals-publisher