Unused member variable in GlossaryViewTest

That's straight forward. Thanks @zaporylie.

Looks like this was indeed added in a new test in #2600804: AJAXified glossary view arguments fail when Language URL detection enabled and didn't really seem to exist before then.

Alright, I checked and confirmed this isn't used anywhere. There's a few other tests that have a similar variable that is actually used.

In core/modules/taxonomy/tests/src/Functional/Views/TaxonomyTermViewTest.php, there's a similar local language variable that's saved and never used; it could be updated like this one is. I thought about whether we should do that in the same patch, but since the Glossary view one is a class member and could actually affect child tests on the off-chance there were any, I think it makes sense to have separate issues. I committed this one to 8.5.x only for that reason. We can add a followup for the Taxonomy view.

Thanks @zaporylie!