Remove dastSiteValidation field from project

What does this MR do?

this merge request removes the field dastSiteValidation from project.

Why?

the process for creating a dast_site_validation previously happened in a single user interaction. as a result, the frontend would need to look up whether or not a dast_site_validation already existed in order to determine what the next most meaningful action a user should take. as this flow has been separated into two distinct creation and validation steps this field is no longer required.

Related Issue(s)

• #289800 (closed)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry behind 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