Remove feature flag for zoom quick actions on issues

What does this MR do?

This enables zoom quick actions by default. Previously they could be enabled or disabled via a feature flag added in this issue:

#31103 (closed)

Development Process:

1. Enabled the feature and checked that it was working on my dev stack
2. Disabled the feature and confirmed that it was no longer working on my dev stack
3. Removed feature flag
4. Confirmed that commenting /zoom <zoom_url> on an issue was working on my dev stack again

WIP because the checklist is not complete.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Performance 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

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

Part of issue #32133 (closed)