Revert "metadata: complain if link url isn't a url"
Revert "metadata: complain if link url isn't a url"

I already tried this once. It had to be reverted because Maintainer Notes
often don't obey this. I had forgotten.

This reverts commit 97ba94903e8896ed9c3b2c8980d218141a5fbdb0.

f-droid/fdroidserver,fdroidtravis/fdroidserver,f-droid/fdroid-server,f-droid/fdroidserver,fdroidtravis/fdroidserver,f-droid/fdroid-server,fdroidtravis/fdroidserver,f-droid/fdroidserver,f-droid/fdroidserver,f-droid/fdroidserver,f-droid/fdroid-server,f-droid/fdroid-server,f-droid/fdroid-server,fdroidtravis/fdroidserver