Remove unused filtered_languages column (#18533)

* Remove unused `filtered_languages` column

Fixes #18522

* Fix tests

db/post_migrate/20220527114923_remove_filtered_languages_from_users.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+
+class RemoveFilteredLanguagesFromUsers < ActiveRecord::Migration[6.1]
+  disable_ddl_transaction!
+
+  def change
+    safety_assured do
+      remove_column :users, :filtered_languages, :string, array: true, default: [], null: false
+    end
+  end
+end