remote: allow `guess_remote_head()` to suppress advice

remote: allow `guess_remote_head()` to suppress advice

The `repo_default_branch_name()` invoked through `guess_remote_head()`
is configured to always display the default branch advice message.

Adapt `guess_remote_head()` to accept flags and convert the `all`
parameter to a flag. Add the `REMOTE_GUESS_HEAD_QUIET` flag to to enable
suppression of advice messages. Call sites are updated accordingly.

Signed-off-by: Justin Tobler <jltobler@gmail.com>
Acked-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>