[CONTINUUM-2222] do not remove POM on error

This was probably in place due to reading temporary files, but all callers into this method are
providing POMs from the working copy. Let the caller delete it if it notices an error and it
passed a temporary file instead

git-svn-id: https://svn.apache.org/repos/asf/continuum/trunk@1594454 13f79535-47bb-0310-9956-ffa450edef68