Remove deprecated features marked for removal in v11

[colinrotherham]

In the later v9.x releases we marked various features with:

/// @deprecated To be removed in v11.0, replaced by xxxx

Similar to #1406 we should remove these before the v11.0.0 release

[colinrotherham]

We also fixed the BEM syntax for icons in #1521

Backwards compatibility was maintained, but should we also remove this in v11?

- .nhsuk-icon__arrow-right-circle,
  .nhsuk-icon--arrow-right-circle {