RFC 211: repo-updater new syncer doesn't use s.Logger

Created by: keegancsmith

This is something I missed in my review. It is directly using log15 globals. But syncer has a Logger passed in that should be used instead.

Additionally the code now has a Info level log which is a bit spammy for info that isn't that useful. I suggest those should be Debug. See https://github.com/sourcegraph/sourcegraph/pull/13717