Hide "Actions" field when there are no buttons to display [RUN AS-IF-FOSS]

What does this MR do?

Part of &4233 (closed)

I have been working of converting the group members view from HAML to Vue over the last two milestones. This MR hides the "Actions" column for users that do not have permissions needed to update or delete members. The buttons themselves are already hidden based on permissions but the column is always shown which leaves some unneeded whitespace sometimes.

Currently this is behind the vue_group_members_list feature flag. To enable:

1. bin/rails console
2. Feature.enable(:vue_group_members_list)

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Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
  • Not needed, behind a feature flag
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team