Stop recording branch.*.remote to '.' for local parents.

We should be using the remote name of the remote branch in
branch.*.merge, instead of the local one as we currently do (I'll
ensure this in a later patch).

As a consequence, setting "remote" to '.' and "merge" to the name of a
*local* parent would become inconsistent with the remote case.  Anyway
the local case should make use of pull-policy=rebase instead, and this
change revealed that we were fetching useless information in the local
case (no need for a remote).

Signed-off-by: Yann Dirson <ydirson@altern.org>