Remove unused warning in pipeline graph

What does this MR do?

Removes unused code in the pipeline graph relating to alert. We had both warnings and errors before, but now, we only have errors. We had a conditional that returned this.warning if there were no errors, but this.warning doesn't exist anymore 😅 . Also because we already have a check on hasErrors, there was no point in keeping the computed prop for alert().

Because this isn't a user facing change, it doesn't require a changelog.

Screenshots (strongly suggested)

Nothing has changed, so here are some screenshots that show everything is as usual after the change

When it's empty

When it's invalid

When it's valid

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines

Availability and Testing

All tests still pass