coreutils: disable documentation build

coreutils: disable documentation build

The makeinfo utility may not be installed on the build machine, and we don't
install documentation anyway.

Fixes:
http://autobuild.buildroot.net/results/b42/b42ceb3128ed832f0dd901a1db8fa3dfd92ce5ef/
http://autobuild.buildroot.net/results/94f/94fcd06b320374f46b340f516c54b7ca726041af/
http://autobuild.buildroot.net/results/c54/c54608ac7e03f14055e2912cf06f6d41d21227c0/

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Tested-by: Karoly Kasza <kaszak@gmail.com>
Acked-by: Karoly Kasza <kaszak@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>