Refactor sync_environment methods

* Add delete_environment method
* Change return value to allow raising an exception

lib/runner/strategy.rb

@@ -13,6 +13,10 @@ class Runner::Strategy
     raise NotImplementedError
   end
 
+  def self.remove_environment(_environment)
+    raise NotImplementedError
+  end
+
   def self.request_from_management(_environment)
     raise NotImplementedError
   end