Remove obsolete tutorial name search field

[fosterfarrell9]

In our User model, we have the following searchable related to Solr searches:

searchable do
  text :tutorial_name
end

There is however no longer any Solr based search for users (and has not been for a long time). The search field was introduced in this commit, and at a later time the search field was changed to tutorial_name. However, this was only used in the users controller in a list method which no longer exists. All user based searches have long since been changed to Postgres searches. If you search for Sunspot.new_search in our code base, you will see that there are no longer any Solr based searches on the user model.
Consequently, this PR removes the obsolete searchable field from the User model.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 54.27%. Comparing base (9dcd2b9) to head (f6caf09).

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #728      +/-   ##
==========================================
- Coverage   54.28%   54.27%   -0.02%     
==========================================
  Files         170      170              
  Lines        7346     7344       -2     
==========================================
- Hits         3988     3986       -2     
  Misses       3358     3358              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[Splines]

Nice! I've searched for various combinations of user and search and didn't find any remnants.

Please squash and merge after the tests have run through.