Extract login utils out of two_factor view

This better reflects how the code is reused in other views and is
not specific to two factor actions. We have a pattern of testing
utility functionality for each view (as opposed to testing the util
+ the view calls the util), so I'm leaving the tests as-is.

app/main/views/new_password.py

@@ -14,8 +14,8 @@ from notifications_utils.url_safe_token import check_token
 
 from app.main import main
 from app.main.forms import NewPasswordForm
-from app.main.views.two_factor import log_in_user
 from app.models.user import User
+from app.utils.login import log_in_user
 
 
 @main.route('/new-password/<path:token>', methods=['GET', 'POST'])