[Task]: Remove Git Extraction Code

[chrstinalin]

Description

Following the decommission of code-manager.

Acceptance Criteria

Milestones/checkpoints

Beta Give feedback

1. Git extraction functionality is removed.
2. Reviewers API to retrieve code for a version and related code is removed
3. Documentation is updated

Checks

• If I have identified that the work is specific to a repository, I have removed "repository:addons-server" or "repository:addons-frontend"

┆Issue is synchronized with this Jira Task

[diox]

In terms of API, the following should be removed:

• List Versions
• Browse
• Compare
• Drafting Comments

For the git extraction part, everything relying on libgit/pygit2 should be removed.

[KevinMind]

Also remove "git" from debian_packages.txt