Move sysutils/bsdcrashtar from GOOGLE_CODE to GitHub

Summary:
This port is too useful to be removed. Since the author has already moved the
project from Google Code to GitHub I think this port should follow.

Test Plan:

• portlint -A: OK
• poudriere testport (all supported tier-1 arch): OK

Reviewers: trociny

Reviewed By: trociny

Subscribers: mat

Differential Revision: https://reviews.freebsd.org/D9885