astro/garmindev: unbreak and set EXPIRES

This port is an add-on to the long expired astro/qlandkartegt (removed
in March 2019). Set expiry to the reasonable near future. While here,
point MASTER_SITES to the SF mirror of qlandkarte/qmapshack (the original
Bitbucket repository has been deleted), just in case anyone wants to
pick it up.