Remove instructlab e2e tests from SDG CI suite

[bbrowning]

The instructlab/instructlab repository depends on SDG, but we have an awkward situation where SDG also installs instructlab/instructlab from latest main and runs the InstructLab e2e tests as part of every PR and in scheduled runs. This creates a circular dependency on instructlab core where we end up having to constantly adapt to any changes in the instructlab e2e suite that are not relevant to our codebase and all of our CI jobs get slowed down by running a plethora of ilab tests unrelated to SDG.

Instead, we need to analyze what parts of SDG are testing by the instructlab e2e tests and ensure those get tested in an SDG-specific test suite. The eventual goal will be to not run the instructlab e2e tests in this repo at all, and rely only on our SDG test suite to verify correctness of our code and interfaces.