Remove feature flag optimize_issue_filter_assigned_to_self

This has already been enabled on production for 4 days without issues so
we can probably remove it now.

app/finders/issues_finder.rb

@@ -48,13 +48,11 @@ class IssuesFinder < IssuableFinder
   def with_confidentiality_access_check
     return Issue.all if params.user_can_see_all_confidential_issues?
 
-    if Feature.enabled?(:optimize_issue_filter_assigned_to_self, default_enabled: :yaml)
-      # If already filtering by assignee we can skip confidentiality since a user
-      # can always see confidential issues assigned to them. This is just an
-      # optimization since a very common usecase of this Finder is to load the
-      # count of issues assigned to the user for the header bar.
-      return Issue.all if current_user && params.assignees.include?(current_user)
-    end
+    # If already filtering by assignee we can skip confidentiality since a user
+    # can always see confidential issues assigned to them. This is just an
+    # optimization since a very common usecase of this Finder is to load the
+    # count of issues assigned to the user for the header bar.
+    return Issue.all if current_user && params.assignees.include?(current_user)
 
     return Issue.where('issues.confidential IS NOT TRUE') if params.user_cannot_see_confidential_issues?
 

changelogs/unreleased/57073-remove-ff-optimize_issue_filter_assigned_to_self.yml

+---
+title: Remove feature flag optimize_issue_filter_assigned_to_self
+merge_request: 57775
+author:
+type: performance

config/feature_flags/development/optimize_issue_filter_assigned_to_self.yml

----
-name: optimize_issue_filter_assigned_to_self
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/57073
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/325470
-milestone: '13.11'
-type: development
-group: group::global search
-default_enabled: false

spec/support/shared_examples/finders/assignees_filter_shared_examples.rb

 # frozen_string_literal: true
 
 RSpec.shared_examples 'assignee ID filter' do
-  context 'when optimize_issue_filter_assigned_to_self is disabled' do
-    before do
-      stub_feature_flags(optimize_issue_filter_assigned_to_self: false)
-    end
-
-    it 'returns issuables assigned to that user' do
-      expect(issuables).to contain_exactly(*expected_issuables)
-    end
-  end
-
   it 'returns issuables assigned to that user' do
     expect(issuables).to contain_exactly(*expected_issuables)
   end
@@ -23,16 +13,6 @@ RSpec.shared_examples 'assignee NOT ID filter' do
 end
 
 RSpec.shared_examples 'assignee username filter' do
-  context 'when optimize_issue_filter_assigned_to_self is disabled' do
-    before do
-      stub_feature_flags(optimize_issue_filter_assigned_to_self: false)
-    end
-
-    it 'returns issuables assigned to those users' do
-      expect(issuables).to contain_exactly(*expected_issuables)
-    end
-  end
-
   it 'returns issuables assigned to those users' do
     expect(issuables).to contain_exactly(*expected_issuables)
   end