tests/test_webdriver: remove assertion on exception message

Asserting on the message that we don't control is prone to break
every time we upgrade selenium, just like I'm doing now.

tests/test_webdriver.py

@@ -21,11 +21,9 @@ def test_webdriver_local_driver_not_present(browser_name):
     else:
         service = FirefoxService(executable_path="failpath")
 
-    with pytest.raises(WebDriverException) as e:
+    with pytest.raises(WebDriverException):
         Browser(browser_name, service=service)
 
-    assert "Message: 'failpath' executable needs to be in PATH." in str(e.value)
-
 
 @pytest.mark.parametrize("browser_name", supported_browsers)
 def test_attach_file(request, browser_name):