PERF: don't recompile css files that have already been compiled

lib/tasks/assets.rake

@@ -72,16 +72,18 @@ task 'assets:precompile:before' do
 end
 
 task 'assets:precompile:css' => 'environment' do
+  puts "Start compiling CSS: #{Time.zone.now}"
   RailsMultisite::ConnectionManagement.each_connection do |db|
     # Heroku precompiles assets before db migration, so tables may not exist.
     # css will get precompiled during first request instead in that case.
     if ActiveRecord::Base.connection.table_exists?(ColorScheme.table_name)
       puts "Compiling css for #{db}"
       [:desktop, :mobile].each do |target|
-        puts DiscourseStylesheets.compile(target, force: true)
+        puts DiscourseStylesheets.compile(target)
       end
     end
   end
+  puts "Done compiling CSS: #{Time.zone.now}"
 end
 
 def assets_path