Remove LTR debug values

These could be viewed in finder pages by appending `&debug_score=1` to the query string.

Finder-frontend attempts to access these defensively, so they are safe to remove.

[Learning to rank is being removed since this change](#2905)

lib/search/presenters/result_presenter.rb

@@ -89,12 +89,6 @@ def add_debug_values(result)
       # debugging is requested, so it's nicer to be explicit about what score
       # it is.
       result[:es_score] = raw_result["_score"]
-      # LearnToRank generated values
-      if RelevanceHelpers.ltr_enabled?
-        result[:model_score] = raw_result["model_score"]
-        result[:original_rank] = raw_result["original_rank"]
-        result[:combined_score] = raw_result["combined_score"]
-      end
 
       result[:_id] = raw_result["_id"]