Don't deploy `latest` lib injection images from `release/2.x`

[andrewlock]

[!IMPORTANT]
This PR should be rebased onto release/2.x once that branch is created. It should not be merged into master

Summary of changes

Removes the "deploy latest" stage for lib-injection when we're in the release/2.x branch

Reason for change

We don't want to mark v2 releases as "latest" once we start releasing v3

Implementation details

Remove those stages

Test coverage

Not much to

Other details

Needs to rebased onto release/2.x