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

one would think so; this is how it was at [L459](https://github.com/apache/spark/pull/2848/files#diff-d239aee594001f8391676e1047a0381eL459), [L477](https://github.com/apache/spark/pull/2848/files#diff-d239aee594001f8391676e1047a0381eL477), and [L506](https://github.com/apache/spark/pull/2848/files#diff-d239aee594001f8391676e1047a0381eL506). Not obvious to me what the original intent was but I'll try to figure it out and do something more sensible.