Drop the Heroku generator's dead code and refresh its USAGE

lib/generators/ember/heroku/USAGE

@@ -1,11 +1,16 @@
 Description:
     Configures a project for deploying to Heroku.
 
-    Once the generator is complete, execute the following:
+    Once the generator is complete, add the buildpacks the deploy needs:
 
         $ heroku buildpacks:clear
         $ heroku buildpacks:add --index 1 heroku/nodejs
         $ heroku buildpacks:add --index 2 heroku/ruby
+
+    `SKIP_EMBER` skips the build wherever it is set. Unset it on the Heroku
+    application, so that `assets:precompile` compiles the EmberCLI
+    applications at deploy time:
+
         $ heroku config:unset SKIP_EMBER
 
 Example:
@@ -16,3 +21,9 @@ Example:
 
     This will create:
         package.json
+
+    An application configured with `yarn` also creates:
+        yarn.lock
+
+    Run the generator again whenever you add an EmberCLI application: the
+    generated `cacheDirectories` names each application's `node_modules`.

lib/generators/ember/heroku/heroku_generator.rb

@@ -38,12 +38,6 @@ def project_root_cached_directories
       [Rails.root.join("node_modules")]
     end
 
-    def app_paths
-      EmberCli.apps.values.map do |app|
-        app.root_path.relative_path_from(Rails.root)
-      end
-    end
-
     def apps
       EmberCli.apps.values
     end

spec/generators/ember/init/init_generator_spec.rb

@@ -0,0 +1,23 @@
+require "generator_spec"
+require "generators/ember/init/init_generator"
+
+describe EmberCli::InitGenerator, type: :generator do
+  destination Rails.root.join("tmp", "init_generator_test_output")
+
+  it "generates an initializer that configures an application" do
+    prepare_destination
+
+    run_generator
+
+    expect(destination_root).to have_structure {
+      directory "config" do
+        directory "initializers" do
+          file "ember.rb" do
+            contains "EmberCli.configure"
+            contains "c.app :frontend"
+          end
+        end
+      end
+    }
+  end
+end