Add option to suppress feedback messages

This is used to dynamically exclude some test results from being shown to users, but still allows them to run in the background (e.g., for research).

app/models/submission.rb

@@ -283,7 +283,7 @@ class Submission < ApplicationRecord
     end
 
     output.merge!(assessment)
-    output.merge!(filename:, message: feedback_message(file, output), weight: file.weight)
+    output.merge!(filename:, message: feedback_message(file, output), weight: file.weight, hidden_feedback: file.hidden_feedback)
     output.except!(:messages)
   end
 
@@ -329,12 +329,6 @@ class Submission < ApplicationRecord
       end
     end
 
-    # Return all test results except for those of a linter if not allowed
-    show_linter = Python20CourseWeek.show_linter? exercise
-    outputs&.reject do |output|
-      next if show_linter || output.blank?
-
-      output[:file_role] == 'teacher_defined_linter'
-    end
+    outputs&.reject {|output| output[:hidden_feedback] if output.present? }
   end
 end