WIP: Remove snapshot flow

What does this MR do?

#209988 (closed)

It appears the snapshot for syncing repositories hasn't been working for a while.

It appears this doesn't surface that often because:

• when there is no error during snapshot, we unset redownload, so further retries use git fetch flow
• when there is an error during snapshot, the fallback is to go back to git fetch into an empty dir

It is possible for some repos to get stuck in redownload flow without an erroring snapshot method, however, which is a serious problem for those repos since the snapshot method doesn't work.

This MR removes the snapshot method since it doesn't appear to be necessary, and would fix those repos stuck in redownload flow.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team