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

slapos/testing/check_software.py

@@ -68,7 +68,6 @@ def checkSoftware(slap, software_url):
       'libgcc_s',
       'libgomp',
       'libm',
-      'libnsl',
       'libpthread',
       'libthread_db',
       'libresolv',