Make db:test:prepare a noop (at least for now)

Previously, running rake spec would always

  (1) create
  (2) auto_migrate!
  (3) seed

the database because db:test:prepare was coded to
do that. Then the spec_helper would have contained
another auto_migrate! command typically.

The proper behavior would probably be to at least
check for pending migrations, but this is not yet
implemented.

Making db:test:prepare a noop for now seems like a
reasonable way, because it gives full control over
auto_migrate! / auto_upgrade! to the spec_helper.rb
and this is how it's typically handled with DM.

lib/dm-rails/railties/database.rake

@@ -6,10 +6,6 @@ namespace :db do
   desc 'Create the database, load the schema, and initialize with the seed data'
   task :setup => [ 'db:create', 'db:automigrate', 'db:seed' ]
 
-  namespace :test do
-    task :prepare => ['db:setup']
-  end
-
   namespace :create do
     desc 'Create all the local databases defined in config/database.yml'
     task :all => :environment do