Custom user fields used to restrict access incorrectly using get_string for field name

1. Make sure conditional activities is switched on in advanced settings;
2. Set up a custom profile field eg "asdf 001";
3. Set up an activity/resource in a course;
4. Restrict access based on the custom user profile field eg "asdf 001" contains "bla"
5. Save and return to course.
6. The condition information will include an incorrect reference to [[asdf 001]]

Code should use API to retrieve field name from the user_info_field table, not a call to get_string()