Add capability to delete site profile from DAST on-demand library

What does this MR do?

It allows a user to delete a site profile from within the on-demand scanner library page.

Screenshots

description	screen
recording of deletion	Kapture_2020-08-07_at_10.29.53
error message

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry (Behind feature flag)
• [-] Documentation ([if required] (https://docs.gitlab.com/ee/development/documentation/workflow.html#when-documentation-is-required)) (captured separate issue)
• 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

Related to #229516 (closed)