Helper cleanup (#1348)

* Remove unused helper files

* Add coverage for application helper

* Add coverage for StreamEntriesHelper #display_name

spec/helpers/stream_entries_helper_spec.rb

@@ -2,7 +2,17 @@ require 'rails_helper'
 
 RSpec.describe StreamEntriesHelper, type: :helper do
   describe '#display_name' do
-    pending
+    it 'uses the display name when it exists' do
+      account = Account.new(display_name: "Display", username: "Username")
+
+      expect(helper.display_name(account)).to eq "Display"
+    end
+
+    it 'uses the username when display name is nil' do
+      account = Account.new(display_name: nil, username: "Username")
+
+      expect(helper.display_name(account)).to eq "Username"
+    end
   end
 
   describe '#avatar_for_status_url' do