Don't recommend to precompile all assets

It is very slow since it will precompile even plugins.

Also it is very unlikely that any application will use this patterns
since it is not a good practice to include all assets manually in the
page.

[ci skip]

guides/source/asset_pipeline.md

@@ -727,27 +727,6 @@ include, you can add them to the `precompile` array in `config/initializers/asse
 Rails.application.config.assets.precompile += ['admin.js', 'admin.css', 'swfObject.js']
 ```
 
-Or, you can opt to precompile all assets with something like this:
-
-```ruby
-# config/initializers/assets.rb
-Rails.application.config.assets.precompile << Proc.new do |path|
-  if path =~ /\.(css|js)\z/
-    full_path = Rails.application.assets.resolve(path).to_path
-    app_assets_path = Rails.root.join('app', 'assets').to_path
-    if full_path.starts_with? app_assets_path
-      logger.info "including asset: " + full_path
-      true
-    else
-      logger.info "excluding asset: " + full_path
-      false
-    end
-  else
-    false
-  end
-end
-```
-
 NOTE. Always specify an expected compiled filename that ends with .js or .css,
 even if you want to add Sass or CoffeeScript files to the precompile array.