At least Fedora 28 glibc-2.27-8.fc28 no longer provides the nis development
headers and libraries.  (It only still contains some binaries for backwards
compatibility, in the libnsl sub-package: "This package provides the legacy
version of libnsl library, for accessing NIS services.")

There is probably no real need to have nis.cpython-*m.so contained in
external/python3/ExternalPackage_python3.mk (it probably just happened to build
fine when that list was originally created, so was included).

Change-Id: Ic6128fd872432005c0ded76640c5b56781ca69a1
Reviewed-on: https://gerrit.libreoffice.org/52535Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>