advice: don't pointlessly suggest --convert-graft-file

advice: don't pointlessly suggest --convert-graft-file

The advice to run 'git replace --convert-graft-file' added in
f9f99b3f7d ("Deprecate support for .git/info/grafts", 2018-04-29)
didn't add an exception for the 'git replace --convert-graft-file'
codepath itself.

As a result we'd suggest running --convert-graft-file while the user
was running --convert-graft-file, which makes no sense. Before:

    $ git replace --convert-graft-file
    hint: Support for <GIT_DIR>/info/grafts is deprecated
    hint: and will be removed in a future Git version.
    hint:
    hint: Please use "git replace --convert-graft-file"
    hint: to convert the grafts into replace refs.
    hint:
    hint: Turn this message off by running
    hint: "git config advice.graftFileDeprecated false"

Add a check for that case and skip printing the advice while the user
is busy following our advice.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>