SW: drop ifenslave from GRML_SMALL and GRML_FULL

Quoting /usr/share/doc/ifenslave/NEWS.Debian.gz:

| ifenslave (2.10) unstable; urgency=medium
|
|   This version of the ifenslave package no longer provides /sbin/ifenslave. The
|   /sbin/ip command from the iproute2 package supports creating bonding masters
|   and enslaving other interfaces to it.
|
|  -- Guus Sliepen <guus@debian.org>  Tue, 08 May 2018 22:47:07 +0200

ifenslave is no longer in Debian/testing since 2021-09-14 due to RC
bugs, and therefore we don't have any recent Debian/testing based daily
ISOs anymore. Given that iproute2 supports network bonding, let's drop
ifenslave from our package list.

Related to grml/grml#148

etc/grml/fai/config/package_config/GRML_FULL

@@ -159,7 +159,6 @@ dnsutils
 ethstatus
 ethtool
 hostapd
-ifenslave
 iftop
 ifupdown
 ipcalc

etc/grml/fai/config/package_config/GRML_SMALL

@@ -30,7 +30,6 @@ gddrescue
 grml-paste
 grml-quickconfig-standard
 htop
-ifenslave
 ifupdown
 imvirt
 iperf3