Remove deprecate_scan_result_policies from violations and workers

What does this MR do and why?

This is part 2 of a 3-MR stack splitting !251778 (closed). It targets MR 1's branch (!252700 (merged)) and merges after MR 1; MR 3, which deletes the flag definition, targets this MR's branch and merges last.

It collapses the remaining Feature.enabled?(:deprecate_scan_result_policies, ...) branches in violation-handling and background-worker code to the enabled path. It also removes ActiveRecord scopes whose only remaining callers are the collapsed branches, and drops the remaining scan_result_policy fallbacks in these paths: the || scan_result_policy_reads OR-checks in the project policy checks, the || violation.scan_result_policy_id fallback in the violation comment service, and the scan_result_policy_id member of the violation details struct. The table stays load-bearing only for the violations upsert key and the any_merge_request read enumeration, which need a unique index on (approval_policy_rule_id, merge_request_id) before they can switch (tracked in the table-drop work item below).

Changes:

• Collapses FF branches in Project#has_approval_policy_rules? / #approval_policy_rules_targeting_commits? (now checking approval_policy_rules only, no reads fallback), ScanResultPolicyViolation#bot_message_disabled?, Security::ScanResultPolicies::PolicyViolationDetails, both UnenforceablePolicyRules*Workers, UpdateViolationsService, CreateViolationDetailsService, UnblockFailOpenApprovalRulesService, SyncAnyMergeRequestRulesService, FallbackBehaviorTrackingService, PolicyViolationCommentGenerator, GeneratePolicyViolationCommentService.
• Deletes ApprovalRuleLike.with_scan_result_policy_read, SoftwareLicensePolicy.with_scan_result_policy_read, and ScanResultPolicyViolation.{for_approval_rules, including_scan_result_policy_reads, for_merge_request_and_scan_result_policies} — their last callers go away here. No indexes or migrations are touched; remaining query paths are unchanged.
• GeneratePolicyViolationCommentService matches rules by approval_policy_rule_id only; UnblockFailOpenApprovalRulesService drops the read preload; PolicyViolationDetails::Violation no longer carries scan_result_policy_id.
• Updates ~12 spec files (removes FF-disabled contexts) and a query-count comment in spec/requests/api/members_spec.rb.

References

• #510282 (closed)
• #617802

Zero-downtime deployment safety

The flag is explicitly enabled on GitLab.com, so old-version nodes still evaluating Feature.enabled? take the same enabled path during a rolling deploy; no migrations or schema changes are involved.

MR acceptance checklist

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