Updated release-process to use github-release.sh

Summary: We have a script to do this step now.

Test Plan:
Try a dry-run yourself:
./github-release.sh -a <asset dir> -t <some release tag> -o <oauth file> -d

Reviewers: #bitcoin_abc, deadalnix, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D4181