Fix non-CYW32 Ethernet connections

Accidentally defined CYW43_SUPPORTED for all boards, not just the ones with
a CYW43 chip onboard.

Author: earlephilhower

lib/platform_def.txt

@@ -63,7 +63,6 @@
 -DPICO_BUILD=1
 -DPICO_COPY_TO_RAM=0
 -DPICO_CYW43_ARCH_THREADSAFE_BACKGROUND=1
--DPICO_CYW43_SUPPORTED=1
 -DPICO_NO_BINARY_INFO=1
 -DPICO_NO_FLASH=0
 -DPICO_NO_HARDWARE=0