Move suite runner deletion to its own function

[t-persson]

Description

We delete suite runners right after setting the Suite runner finished condition. If that, for some reason, fails we will never try to delete the suite runner again.
Move the deletion to its own function with its own checks so that we delete stale suite runners on each reconciliation.

Additional Context

No response

Further links

https://github.com/eiffel-community/etos/blob/main/internal/controller/testrun_controller.go#L331