Remove things deprecated as part of v4.x releases

[36degrees]

What

Remove anything that we've deprecated as part of a v4 release, except those things already covered by our other epics:

• Reduce Internet Explorer (IE) support in GOV.UK Frontend #2621
• Remove compatibility mode #2769

Why

As a general rule, once something has been deprecated we should remove it in the next major release. Tidying up after ourselves helps to keep the codebase maintainable.

Done when

In v5.0

Beta Give feedback

1. Remove deprecated govuk-header__link--service-name class #2636
   breaking change header +2
   
2. Remove deprecated .govuk-header__navigation--no-service-name class #2695
   breaking change header +2
   
3. Header component CSS is accounting for users not building the header component correctly #2746
   tech debt 🕔 hours +2
   
4. Remove deprecated govuk-!-margin-static and govuk-!-padding-static classes #2782
   breaking change sass / css +2
   
5. Remove deprecated govuk-button--disabled class #2681
   accessibility accessibility-concern breaking change button +4
   

[querkmachine]

This looks like it's done now! 🎉