Remove needless `silence_warnings`

Since ff30db13, warning is not shown.

railties/test/application/asset_debugging_test.rb

@@ -9,10 +9,7 @@ class AssetDebuggingTest < ActiveSupport::TestCase
     include Rack::Test::Methods
 
     def setup
-      # FIXME: shush Sass warning spam, not relevant to testing Railties
-      Kernel.silence_warnings do
-        build_app(initializers: true)
-      end
+      build_app(initializers: true)
 
       app_file "app/assets/javascripts/application.js", "//= require_tree ."
       app_file "app/assets/javascripts/xmlhr.js", "function f1() { alert(); }"
@@ -36,11 +33,6 @@ def teardown
       teardown_app
     end
 
-    # FIXME: shush Sass warning spam, not relevant to testing Railties
-    def get(*)
-      Kernel.silence_warnings { super }
-    end
-
     test "assets are concatenated when debug is off and compile is off either if debug_assets param is provided" do
       # config.assets.debug and config.assets.compile are false for production environment
       ENV["RAILS_ENV"] = "production"

railties/test/application/assets_test.rb

@@ -62,10 +62,7 @@ def assert_no_file_exists(filename)
 
       add_to_env_config "development", "config.assets.digest = false"
 
-      # FIXME: shush Sass warning spam, not relevant to testing Railties
-      Kernel.silence_warnings do
-        require "#{app_path}/config/environment"
-      end
+      require "#{app_path}/config/environment"
 
       get "/assets/demo.js"
       assert_equal 'a = "/assets/rails.png";', last_response.body.strip

railties/test/isolation/abstract_unit.rb

@@ -56,10 +56,7 @@ def app(env = "production")
       @app ||= begin
         ENV["RAILS_ENV"] = env
 
-        # FIXME: shush Sass warning spam, not relevant to testing Railties
-        Kernel.silence_warnings do
-          require "#{app_path}/config/environment"
-        end
+        require "#{app_path}/config/environment"
 
         Rails.application
       end