Simplify and fix name of llama tests

[will-cromar]

Description

The test name currently has the suffix -1vm-1vm. Simplify the test config since there's no 2VM or XRT case to worry about anymore :confetti_ball:

Tests

Diff shows just name changes, e.g.

-              cronjob.batch/pt-nightly-llama2-pjrt-infer-func-v4-8-1vm-1vm
-              cronjob.batch/pt-nightly-llama2-pjrt-train-spmd-func-v4-8-1vm-1vm
+              cronjob.batch/pt-nightly-llama2-infer-func-v4-8-1vm
+              cronjob.batch/pt-nightly-llama2-train-spmd-func-v4-8-1vm

Checklist

Before submitting this PR, please make sure (put X in square brackets):

• [x] I have performed a self-review of my code.
• [x] I have necessary comments in my code, particularly in hard-to-understand areas.
• [x] I have run one-shot tests and provided workload links above if applicable.
• [x] I have made or will make corresponding changes to the doc if needed.