Always Show Delete Button on Feature Flag Strategies

What does this MR do?

Always show the delete button on a feature flag strategy, even when there is only one strategy.

Previously, the UI enforced a flag having at least one strategy by hiding the delete button when there was only one strategy.

This also fixes the original bug described in the issue where sometimes the delete button would be displayed even when there was only a single strategy.

Issue: #223209 (closed)

Screenshots

Before:

After:

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• 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