completion: add git config advice completions

completion: add git config advice completions

Add missing completions for git config advice:

* advice.amWorkDir
* advice.pushAlreadyExists
* advice.pushFetchFirst
* advice.pushNeedsForce
* advice.pushNonFFCurrent
* advice.pushNonFFMatching
* advice.pushUpdateRejected
* advice.rmHints
* advice.statusUoption

Remove completion for git config advice.pushNonFastForward,
since it was renamed to pushUpdateRejected in 1184564eac8e.
The config still works, but is no longer part of the documentation.

Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>