Remove scanned_resources_count from security scan

What does this MR do?

This MR relates to #231424 (closed)

Currently the DAST report endpoint /namespace/project/-/merge_requests/5/dast_reports returns the scanned resources count and the URL to the job log. They were initially used to show the scanned resources count for DAST jobs in the MR widget but have been replaced by the securityReportSummary GraphQL endpoint.

This MR removes scanned_resources_count and job_path from the dast_reports endpoint. The column scanned_resources_count on Security::Scan will be removed in a subsequent MR.

{
    "base_report_created_at": "2020-03-10T23:34:50.571Z",
    "base_report_out_of_date": true,
    "head_report_created_at": "2020-05-26T03:31:22.097Z",
    "added": [],
    "fixed": [],
    "existing": [],
-   "scans": [
-       {
-           "scanned_resources_count": 14,
-           "job_path": "/craigmsmith/craigmsmith-railsgoat-example/-/jobs/567061221"
-       },
-       {
-           "scanned_resources_count": 14,
-           "job_path": "/craigmsmith/craigmsmith-railsgoat-example/-/jobs/566994377"
-       },
-       {
-           "scanned_resources_count": 14,
-           "job_path": "/craigmsmith/craigmsmith-railsgoat-example/-/jobs/538036908"
-       }
-   ]
}

Screenshots

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