Remove feature flag in Member callback

Remove feature flag logic in Member's callback to update the highest
role that was introduced as a safety until the User callback is in
place.

app/models/member.rb

@@ -470,7 +470,6 @@ class Member < ApplicationRecord
   # for a Member to be commited before attempting to update the highest role.
   # rubocop: disable CodeReuse/ServiceClass
   def update_highest_role
-    return unless Feature.enabled?(:highest_role_callback)
     return unless user_id.present?
     return unless previous_changes[:access_level].present?
 

spec/models/member_spec.rb

@@ -597,7 +597,6 @@ describe Member do
   end
 
   context 'when after_commit :update_highest_role' do
-    context 'with feature flag enabled' do
     where(:member_type, :source_type) do
       :project_member | :project
       :group_member   | :group
@@ -646,51 +645,4 @@ describe Member do
       end
     end
   end
-
-    context 'with feature flag disabled' do
-      before do
-        stub_feature_flags(highest_role_callback: false)
-      end
-
-      where(:member_type, :source_type) do
-        :project_member | :project
-        :group_member   | :group
-      end
-
-      with_them do
-        describe 'create member' do
-          it 'does not initialize a new Members::UpdateHighestRoleService object' do
-            source = create(source_type)
-            user = create(:user)
-
-            expect(Members::UpdateHighestRoleService).not_to receive(:new).with(user.id)
-
-            create(member_type, :guest, user: user, source_type => source)
-          end
-        end
-
-        context 'when member exists' do
-          let!(:member) { create(member_type) }
-
-          describe 'update member' do
-            context 'when access level was changed' do
-              it 'does not initialize a new Members::UpdateHighestRoleService object' do
-                expect(Members::UpdateHighestRoleService).not_to receive(:new).with(member.user_id)
-
-                member.update(access_level: Gitlab::Access::GUEST)
-              end
-            end
-          end
-
-          describe 'destroy member' do
-            it 'does not initialize a new Members::UpdateHighestRoleService object' do
-              expect(Members::UpdateHighestRoleService).not_to receive(:new).with(member.user_id)
-
-              member.destroy
-            end
-          end
-        end
-      end
-    end
-  end
 end