Remove Apollo error suppression feature flag

This removes the `suppress_apollo_errors_during_navigation` feature
flag, as it's been [enabled in production without issue for a week][1].

Addresses https://gitlab.com/gitlab-org/gitlab/-/issues/342745 and
https://gitlab.com/gitlab-org/gitlab/-/issues/335530.

[1]: https://gitlab.com/gitlab-org/gitlab/-/issues/342745#note_720803582

Changelog: changed

app/assets/javascripts/lib/apollo/suppress_network_errors_during_navigation_link.js

@@ -9,10 +9,6 @@ import { isNavigatingAway } from '~/lib/utils/is_navigating_away';
  * @returns {ApolloLink|null}
  */
 export const getSuppressNetworkErrorsDuringNavigationLink = () => {
-  if (!gon.features?.suppressApolloErrorsDuringNavigation) {
-    return null;
-  }
-
   return onError(({ networkError }) => {
     if (networkError && isNavigatingAway()) {
       // Return an observable that will never notify any subscribers with any

config/feature_flags/development/suppress_apollo_errors_during_navigation.yml

----
-name: suppress_apollo_errors_during_navigation
-introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/72031
-rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/342745
-milestone: '14.4'
-type: development
-group: group::foundations
-default_enabled: false

lib/gitlab/gon_helper.rb

@@ -56,7 +56,6 @@ module Gitlab
       push_frontend_feature_flag(:security_auto_fix, default_enabled: false)
       push_frontend_feature_flag(:improved_emoji_picker, default_enabled: :yaml)
       push_frontend_feature_flag(:new_header_search, default_enabled: :yaml)
-      push_frontend_feature_flag(:suppress_apollo_errors_during_navigation, current_user, default_enabled: :yaml)
       push_frontend_feature_flag(:configure_iac_scanning_via_mr, current_user, default_enabled: :yaml)
       push_frontend_feature_flag(:bootstrap_confirmation_modals, default_enabled: :yaml)
     end

spec/frontend/lib/apollo/suppress_network_errors_during_navigation_link_spec.js

@@ -47,17 +47,6 @@ describe('getSuppressNetworkErrorsDuringNavigationLink', () => {
     subscription = link.request(mockOperation).subscribe(observer);
   };
 
-  describe('when disabled', () => {
-    it('returns null', () => {
-      expect(getSuppressNetworkErrorsDuringNavigationLink()).toBe(null);
-    });
-  });
-
-  describe('when enabled', () => {
-    beforeEach(() => {
-      window.gon = { features: { suppressApolloErrorsDuringNavigation: true } };
-    });
-
   it('returns an ApolloLink', () => {
     expect(getSuppressNetworkErrorsDuringNavigationLink()).toEqual(expect.any(ApolloLink));
   });
@@ -151,5 +140,4 @@ describe('getSuppressNetworkErrorsDuringNavigationLink', () => {
       });
     });
   });
-  });
 });