[SPARK-3967] don’t redundantly overwrite executor JAR deps

Hey @ryan-williams my concern is that if the delete fails (e.g. because of some permissions thing), then we will always have an old version of the file because `destFile.exists` will always be true. It might make sense to throw an exception if delete is unsuccessful instead of logging a message up there in L429 that is technically not true (I realize you just moved the code, but it would still be good to fix this).