PSPNG: Group deletion can lead to jexl error

When PSPNG processes changelog entries related to group deletion, it can fail with the following error:

java.lang.RuntimeException: Error in loader job: null, check logs: Error: edu.internet2.middleware.grouper.exception.ExpressionLanguageMissingVariableException: variable 'stemAttributes' is not defined in script: 'utils.containedWithin(provisionerName, stemAttributes['etc:pspng:provision_to'], groupAttributes['etc:pspng:provision_to']) && !utils.containedWithin(provisionerName, stemAttributes['etc:pspng:do_not_provision_to'], groupAttributes['etc:pspng:do_not_provision_to'])'

This leads to the pspng's changelog-processing being stuck and having to moved beyond the failed unprocessable entry.