sync: Disable info about disabling pruning when quiet

If you have a lot of shared projects, it spams.

Bug: https://crbug.com/gerrit/13961
Change-Id: If3f5baef65930830af9a2cd01a1b593dd518ab09
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/294049


Tested-by: Anders Björklund <anders.bjorklund.2@volvocars.com>
Reviewed-by: Mike Frysinger <vapier@google.com>