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

This is super-nitpicky of me, but I love to avoid mutability whenever possible, so it would be nice to see if there was a clean way to remove this variable.  It looks like `shouldCopy=false` only in the case where the file contents are the same, so maybe we could just add a `return` on that branch and can remove the `shouldCopy` variable entirely.  This would let us remove the `if` on line 478,