Broken link to the ELCE 2019 presentation

[ekawahyu]

The link seems broken when I tried to download from here. When I checked on ELCE 2019 website, it was not there either.

[Carton32]

The link to documentation of samples/net/wpanusb firmware from Zephyr is also broken but that's part of a bigger issue as the sample was removed from Zephyr a few months ago. As I understand, the project is on standby anyway.