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