LPC408X: Delete the ethernet_api.c files

Remove an obsolete HAL implementation from LPC408X to fix the GCC_ARM
build with the "-flto" flag.

With the lto enabled, unreferenced buffers defined in ethernet_api.c
were not excluded at link time overflowing the 16kB peripheral SRAM1
(ld error: "section '.AHBSRAM1' will not fit in region 'ETH_RAM'").

The Ethernet HAL API is deprecated in favor of EMAC.

Author: Filip Jagodzinski