project.py: Remove extraneous ','

Bug: https://crbug.com/1061473
Change-Id: I0f02f122d6313679c1ae5ad6fb4e05f68b764186
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/263112


Tested-by: George Engelbrecht <engeg@google.com>
Reviewed-by: George Engelbrecht <engeg@google.com>
Reviewed-by: SPA SARC <spanc.sarc@gmail.com>
Reviewed-by: Mike Frysinger <vapier@google.com>