um: remove pcap driver from documentation

We just removed the driver, but forgot the row in the
documentation table mentioning it. Remove that.

Link: https://patch.msgid.link/20240703172013.c3232dc5cbe9.I7f9941095d45a39d0f1e83680a408b3c6d445242@changeid


Acked-By: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>