samples: net: zperf: Remove config files for Galileo board

The support for Galileo board is bitrotted as the config file
contains obsolete values. As testing this old board is difficult
lets remove the config files. These can be re-introduced with
proper and tested settings if needed.

Fixes #7814

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>