Rely on Rails' route method to be correct

Previously, we were searching for a `routes.rb` to verify that we'd
already added the routes or not. We don't need to do this: the `route`
method will only ever inject into the `config/routes.rb` file it knows
about — so us looking elsewhere would never make a difference to the
outcome of the generator.

On top of this, the `route` method in turn leans on `inject_into_file`
from Thor which is configured to not force the result.

So, much of this can go. We just continue to check that we don't
generate routes with no models.

https://github.com/rails/rails/blob/291a3d2ef29a3842d1156ada7526f4ee60dd2b59/railties/lib/rails/generators/actions.rb#L269
https://github.com/erikhuda/thor/blob/34df888d721ecaa8cf0cea97d51dc6c388002742/lib/thor/actions/inject_into_file.rb#L26

lib/administrate/generator_helpers.rb

@@ -4,31 +4,10 @@ def call_generator(generator, *args)
       Rails::Generators.invoke(generator, args, generator_options)
     end
 
-    def find_routes_file
-      routes_file = Rails.root.join("config/routes.rb")
-      if File.exist?(routes_file)
-        routes_file = find_file("routes.rb")
-        raise "Unable to locate your routes.rb file" if routes_file.nil?
-      end
-      routes_file
-    end
-
     private
 
     def generator_options
       { behavior: behavior }
     end
-
-    def find_file(file_name)
-      file = nil
-      Find.find(Rails.root) do |path|
-        Find.prune if path.include? ".git"
-
-        next unless path.include? file_name
-
-        file = path
-      end
-      file
-    end
   end
 end

lib/generators/administrate/routes/routes_generator.rb

@@ -16,7 +16,7 @@ class RoutesGenerator < Rails::Generators::Base
       class_option :namespace, type: :string, default: "admin"
 
       def insert_dashboard_routes
-        if should_route_dashboard?
+        if valid_dashboard_models.any?
           route(dashboard_routes)
         end
       end
@@ -78,21 +78,9 @@ def dashboard_routes
         ERB.new(File.read(routes_file_path)).result(binding)
       end
 
-      def routes_includes_resources?
-        File.read(rails_routes_file_path).include?(dashboard_routes)
-      end
-
-      def rails_routes_file_path
-        find_routes_file
-      end
-
       def routes_file_path
         File.expand_path(find_in_source_paths("routes.rb.erb"))
       end
-
-      def should_route_dashboard?
-        routes_includes_resources? || valid_dashboard_models.any?
-      end
     end
   end
 end