testing/check_software: no longer tolerate system libnsl
Since slapos commit 246be932e (component/libtirpc,libnsl: initial inclusion, 2021-12-28) we have a slapos component, so no reason to accept the system library
Since slapos commit 246be932e (component/libtirpc,libnsl: initial inclusion, 2021-12-28) we have a slapos component, so no reason to accept the system library