Jskinner lg5949 analytics events 28

[jskinne3]

LG-5949
https://cm-jira.usa.gov/browse/LG-5949
analytics events number 28, replaces these 5 constants with methods:

1. BACKUP_CODE_DELETED
2. BACKUP_CODE_SETUP_VISIT
3. BACKUP_CODE_SETUP_SUBMITTED
4. SAML_AUTH
5. SESSION_TIMED_OUT

Found that numbers 1 and 3 were not used; these were simply removed.

Tested with:

bundle exec rspec spec/controllers/users/backup_code_setup_controller_spec.rb
bundle exec rspec spec/controllers/saml_idp_controller_spec.rb
bundle exec rspec spec/controllers/users/sessions_controller_spec.rb

[zachmargolis]

LGTM