Sqservices 1529 remove redundant endpoints internal and view feature permissions

[battermann]

https://wearezeta.atlassian.net/browse/SQSERVICES-1529

Removed the following deprecated internal endpoints, which are neither used within wire-server, nor by ibis, nor by stern:

• PUT i/teams/:tid/features/search-visibility
• GET i/teams/:tid/features/search-visibility
• PUT i/teams/:tid/features/validate-saml-emails
• GET i/teams/:tid/features/validate-saml-emails
• PUT i/teams/:tid/features/digital-signatures
• GET i/teams/:tid/features/digital-signatures

This PR also removes redundant permission checks for viewing features

Checklist

• The PR Title explains the impact of the change.
• The PR description provides context as to why the change should occur and what the code contributes to that effect. This could also be a link to a JIRA ticket or a Github issue, if there is one.
• changelog.d contains the following bits of information (details):
  • A file with the changelog entry in one or more suitable sub-sections. The sub-sections are marked by directories inside changelog.d.

[smatting]

This PR also removes redundant permission checks for viewing features. Can you please update or title of the PR accordingly?