Remove the ifconfig test added in rev 263445.  After discussion with
melifaro, we agreed that ifconfig's behavior was not a bug.  The main
motivation for bin/187551 was to partially resolve kern/187549, but we
resolved kern/187549 in a different way instead.

ObsoleteFiles.inc
etc/mtree/BSD.tests.dist
sbin/ifconfig/tests/fibs_test.sh
sbin/ifconfig/tests/Makefile
sbin/ifconfig/Makefile
	Remove /usr/tests/sbin/ifconfig

PR:		bin/187551
MFC after:	3 days
Sponsored by:	Spectra Logic