linux: remove wrong log attempt

There is neither a "self" nor a "logger". The caller knows that no ip
address has been found as the return value is None, so remove this
without substitution.

Signed-off-by: Bastian Krause <bst@pengutronix.de>

labgridhelper/linux.py

@@ -156,7 +156,6 @@ def get_interface_ip(command, interface="eth0"):
     try:
         ip_string = command.run_check("ip -o -4 addr show")
     except ExecutionError:
-        self.logger.debug('No ip address found')
         return None
 
     regex = re.compile(