Remove 'No suggestions' box from interests or when no official tags exist

Test this fix: (on every supported browser) Edit one of your blog posts and verify the tags field is working correctly. It should show auto-complete suggestions from the official tags list. (Make sure that this works as you type) Edit your profile and verify the interests field is working correctly. It should not show autocomplete suggestions and should not have a down arrow to hint that there are any suggestions. Enable chrome vox and verify that the interests field does not announce itself as a combo box (but does read out the list of current tags as a multiselect thing). Test for refactor: Pick the testing commit from https://github.com/damyon/moodle/commit/9d2d825ccfee19d234c261e4109dfba462dd07e3 and verify all the different autocomplete fields still work correctly on the test page.