Remove Popular recommender

[mdekstrand]

This removes the Popular recommender in favor of PopScore.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.13%. Comparing base (cbfe956) to head (d09db54).
Report is 620 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #420      +/-   ##
==========================================
+ Coverage   90.11%   90.13%   +0.01%     
==========================================
  Files          49       49              
  Lines        3258     3233      -25     
==========================================
- Hits         2936     2914      -22     
+ Misses        322      319       -3     

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