Remove the legacy organisation list, colour palette and $websafe parameter

[querkmachine]

What

Remove the following in a future major release of GOV.UK Frontend:

• the legacy organisation list and colour palette
• the $govuk-new-organisation-colours feature flag
• the $websafe parameter of the govuk-organisation-colour function
• the transitional code that maps $websafe to $contrast-safe in the govuk-organisation-colour function
• tests related to legacy functionality

Why

The legacy organisation list and colour palette has been replaced by a newer version. The legacy list will not receive updates and should be removed.

Who needs to work on this

• Developers

Who needs to review this

• Developers

Done when

• The legacy colour palette has been marked as deprecated
• The $govuk-new-organisation-colours feature flag has been removed
• The $websafe parameter of the govuk-organisation-colour function has been removed
• The transitional code that maps $websafe to $contrast-safe in the govuk-organisation-colour function has been removed
• Tests related to legacy functionality have been removed