Remove unnecessary git-rm --cached reference from status output

Since git-reset has learned restoring the absence of paths git-rm --cached is
no longer necessary. Therefore remove it from the cached content header hint.

Also remove the unfortunate wording 'Cached' from the header itself.

Signed-off-by: Jürgen Rühle <j-r@online.de>
Signed-off-by: Junio C Hamano <junkio@cox.net>