Update the printout message of dynamic agents check to reduce the confusion

Remove the printout message initially for debug and update some code comments to make the dynamic agents logic clearer.

The message of echo dynamicAgents: [azure, fyre] confuses that code is doing the dynamic agent check.
Also the comment https://github.com/adoptium/aqa-tests/blob/master/buildenv/jenkins/openjdk_tests#L212-L214 should be reorganized.

```
[Pipeline] echo
15:34:12 dynamicAgents: [azure, fyre]
[Pipeline] node
15:34:12 Running on [test-equinix_esxi-ubuntu2204-x64-1](https://ci.adoptium.net/computer/test-equinix_esxi-ubuntu2204-x64-1/) in /home/jenkins/workspace/Grinder

```

Start in buildenv/jenkins/openjdk_tests at the linked comment around lines 212-214 and locate the dynamicAgents printout. Remove the initial debug message and reorganize the comment so the dynamic-agent logic is clearer; done when the misleading echo no longer appears and the comment matches the logic.

Written by the indexing model from the issue text.