px4fmu-v2 and px4fmu-v3 boards cleanup

Makefile

src/drivers/boards/px4fmu-v2/CMakeLists.txt

src/drivers/boards/px4fmu-v2/px4fmu_init.c

src/drivers/boards/px4fmu-v2/px4fmu_led.c

src/drivers/boards/px4fmu-v2/px4fmu_usb.c

src/drivers/boards/px4fmu-v3/CMakeLists.txt

src/drivers/boards/px4fmu-v3/px4fmu_init.c

src/drivers/boards/px4fmu-v3/px4fmu_led.c

src/drivers/boards/px4fmu-v3/px4fmu_spi.c