Remove symmetric crypto alt interface

[tom-daubney-arm]

Description

Remove symmetric crypto ALT interfaces.

This PR is made up of commits split out from #9226 in order to ease review.

PR checklist

Please tick as appropriate and edit the reasons (e.g.: "backport: not needed because this is a new feature")

• [x] changelog Will be provided at end of PR series
• [x] 3.6 backport not required
• [x] 2.28 backport not required
• [x] tests existing tests suffice

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