Fix Style/UnneededInterpolation

Exclusions from .rubocop_todo.yml deleted.
This cop checks for string interpolated expressions. It supports autocorrection.
Fixes #1823

.rubocop_todo.yml

@@ -722,10 +722,3 @@ Style/TrailingCommaInLiteral:
     - 'Guardfile'
     - 'db/migrate/20140701123203_add_events_per_week_to_conference.rb'
     - 'spec/models/conference_spec.rb'
-
-# Offense count: 3
-# Cop supports --auto-correct.
-Style/UnneededInterpolation:
-  Exclude:
-    - 'app/helpers/format_helper.rb'
-    - 'spec/controllers/admin/conferences_controller_spec.rb'

app/helpers/format_helper.rb

@@ -122,7 +122,7 @@ module FormatHelper
              plural || singular.pluralize
            end
 
-    "#{word}"
+    word
   end
 
   # Returns black or white deppending on what of them contrast more with the

spec/controllers/admin/conferences_controller_spec.rb

@@ -56,8 +56,8 @@ describe Admin::ConferencesController do
           conference.reload
           expect(flash[:error])
               .to eq("Updating conference failed. Short title can't be blank.")
-          expect(conference.title).to eq("#{conference.title}")
-          expect(conference.short_title).to eq("#{conference.short_title}")
+          expect(conference.title).to eq(conference.title)
+          expect(conference.short_title).to eq(conference.short_title)
         end
 
         it 're-renders the #show template' do