Removed device emac check from emac greentea tests

DEVICE_EMAC is defined only for boards with default Ethernet emac.
It is not defined for example for Realtek RTL8195AM board that
does not have Ethernet. Removed the check for device emac from emac
greentea tests.

Author: Mika Leppänen

TESTS/network/emac/main.cpp

@@ -43,10 +43,6 @@
 #endif
 #endif
 
-#ifndef DEVICE_EMAC
-#error [NOT_SUPPORTED] Device EMAC has to be enabled for the target
-#endif
-
 #include "greentea-client/test_env.h"
 #include "unity.h"
 #include "utest.h"