SW: drop tshark + wireshark from GRML_FULL

libwireshark15 has >100MB Installed-Size, and wireshark plus all its
dependencies currently require 164MB of disk space on grml-full. This
seems to be too much for one specific, non-essential tool, and given we
still ship tcpdump, it makes more sense to reduce ISO size.

tshark depends on wireshark-common, so we need to also drop it.

Related to https://github.com/grml/grml-live/issues/118