Clean model refection for code generation

What does this merge request do and why?

This MR provides support for cleaning model reflection when the code generation mode is activated.

How to set up and validate locally

1. Run the server following the steps in the Readme file.
2. The following prefix causes the model to output duplicates:

   # print hello world
   print('hello world')

Merge request checklist

• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.

Ref: gitlab-org/gitlab#424906 (closed)