Do not generate configuration for sprockets if propshaft is used

Author: javierav

railties/lib/rails/generators/rails/app/templates/config/initializers/assets.rb.tt

@@ -5,8 +5,10 @@ Rails.application.config.assets.version = "1.0"
 
 # Add additional assets to the asset load path.
 # Rails.application.config.assets.paths << Emoji.images_path
+<% if options[:asset_pipeline] == "sprockets" -%>
 
 # Precompile additional assets.
 # application.js, application.css, and all non-JS/CSS in the app/assets
 # folder are already added.
 # Rails.application.config.assets.precompile += %w( admin.js admin.css )
+<% end -%>