BC: Fixed navigation menu when 'Dropdown type is set to 'None'.

[joshua-salsadigital]

closes #96

https://www.drupal.org/project/civictheme/issues/3422805

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Changed

1. Updated navigation to remove child items when dropdown is set to none.
2. Added missing styles for navigation when when dropdown is set to none.

Screenshots

Before:

After:

[github-actions]

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[AlexSkrypnyk]

@joshua-salsadigital
this is great! Thank you for solving it here - the None Dropdown type should be doing what it says on the tin

however, for those users who has potentially used None to apply their own style, this would break their implementation.

We could have introduced Custom type which would be doing what None currently does. But we do not need to do this - any customisations are expected to be using custom twig templates. For this change - those consumers would have to revert their templates to the state before this change. We would need to add a release BC record about this.