Remove enable_adherence_check_for_scanners feature flag

What does this MR do and why?

Remove enable_adherence_check_for_scanners feature flag

This commit removes feature flag enable_adherence_check_for_scanners

Changelog: changed

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Related to #492118 (closed)

doc/user/compliance/compliance_center/compliance_standards_adherence_dashboard.md

@@ -18,6 +18,8 @@ DETAILS:
 > - Standards adherence grouping [introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/413735) in GitLab 16.9.
 > - Standards adherence grouping by standards that a check belongs to and grouping by projects that a check belongs to [added](https://gitlab.com/gitlab-org/gitlab/-/issues/413735) in GitLab 16.10.
 > - **Last Scanned** column [renamed](https://gitlab.com/gitlab-org/gitlab/-/issues/439545) to **Date since last status change** in GitLab 16.10.
+> - DAST scanner check [introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/440721) to GitLab Standard in GitLab 17.6.
+> - SAST scanner check [introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/440722) to GitLab Standard in GitLab 17.6.
 
 The compliance standards adherence dashboard lists the adherence status of projects complying to the _GitLab standard_.