tests: remove erroneous check "up" string in availability test (#76116)

It would catch the old "We recommend you to update your web browser"
from gadjo.

tests/test_manager.py

@@ -477,7 +477,6 @@ def test_availability_parameters(app, admin_user, monkeypatch):
     assert 'Availability check' in resp.text
 
     resp = resp.click('Availability check')
-    assert 'up' in resp.text
     resp.form['run_check'] = False
     resp = resp.form.submit()
     # Connector status not changed, availability parameters changed