rm: introduce advice.rmHints to shorten messages

rm: introduce advice.rmHints to shorten messages

Introduce advice.rmHints to choose whether to display advice or not
when git rm fails. Defaults to true, in order to preserve current behavior.

As an example, the message:
	error: 'foo.txt' has changes staged in the index
	(use --cached to keep the file, or -f to force removal)

would look like, with advice.rmHints=false:
	error: 'foo.txt' has changes staged in the index

Signed-off-by: Mathieu Lienard--Mayor <Mathieu.Lienard--Mayor@ensimag.imag.fr>
Signed-off-by: Jorge Juan Garcia Garcia <Jorge-Juan.Garcia-Garcia@ensimag.imag.fr>
Signed-off-by: Matthieu Moy <Matthieu.Moy@grenoble-inp.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>