zsh: disable NIS support

zsh: disable NIS support

The configure test for NIS and NIS+ looks for the ypcat and nisls host
utilities, respectively. This is not compatible with cross compilation.
Disable both unconditionally.

Fixes:
http://autobuild.buildroot.net/results/54c/54c9c5dff3df0a43573b03896cb0629fcae08478/
http://autobuild.buildroot.net/results/c8e/c8e30a1eb6e77ae76292b6a01bede5abb2b1b7b7/

Cc: Phil Eichinger <phil.eichinger@gmail.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>