branch: drop non-commit error reporting

branch: drop non-commit error reporting

Remove the error "branch '%s' does not point at a commit" in
append_ref(), which reports branch refs which do not point to
commits.  Also remove the error "some refs could not be read" in
print_ref_list() which is triggered as a consequence of the first
error.

The purpose of these codepaths is not to diagnose and report a
repository corruption.  If we care about such a corruption, we
should report it from fsck instead, which we already do.

This also helps in a smooth port of branch.c to use ref-filter APIs
over the following patches. On the other hand, ref-filter ignores refs
which do not point at commits silently.

Based-on-patch-by: Jeff King <peff@peff.net>
Helped-by: Junio C Hamano <gitster@pobox.com>
Mentored-by: Christian Couder <christian.couder@gmail.com>
Mentored-by: Matthieu Moy <matthieu.moy@grenoble-inp.fr>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>