Removed sql_set_operators feature flag

Union set operator now matches intersect and except set operators.

app/models/concerns/from_union.rb

@@ -37,27 +37,6 @@ module FromUnion
     # rubocop: disable Gitlab/Union
     extend FromSetOperator
     define_set_operator Gitlab::SQL::Union
-
-    alias_method :from_union_set_operator, :from_union
-    def from_union(members, remove_duplicates: true, alias_as: table_name)
-      if Feature.enabled?(:sql_set_operators)
-        from_union_set_operator(members, remove_duplicates: remove_duplicates, alias_as: alias_as)
-      else
-        # The original from_union method.
-        standard_from_union(members, remove_duplicates: remove_duplicates, alias_as: alias_as)
-      end
-    end
-
-    private
-
-    def standard_from_union(members, remove_duplicates: true, alias_as: table_name)
-      union = Gitlab::SQL::Union
-        .new(members, remove_duplicates: remove_duplicates)
-        .to_sql
-
-      from(Arel.sql("(#{union}) #{alias_as}"))
-    end
-
     # rubocop: enable Gitlab/Union
   end
 end

changelogs/unreleased/273356-remove-sql_set_operators-feature-flag.yml

+---
+title: Enable refactored union set operator
+merge_request: 46295
+author:
+type: added

config/feature_flags/development/sql_set_operators.yml

----
-name: sql_set_operators
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/39786
-rollout_issue_url:
-group: group::access
-type: development
-default_enabled: false

spec/models/concerns/from_union_spec.rb

@@ -3,13 +3,5 @@
 require 'spec_helper'
 
 RSpec.describe FromUnion do
-  [true, false].each do |sql_set_operator|
-    context "when sql-set-operators feature flag is #{sql_set_operator}" do
-      before do
-        stub_feature_flags(sql_set_operators: sql_set_operator)
-      end
-
-      it_behaves_like 'from set operator', Gitlab::SQL::Union
-    end
-  end
+  it_behaves_like 'from set operator', Gitlab::SQL::Union
 end