delete px4_includes.h header and update boards/ to use syslog

boards/airmind/mindpx-v2/src/init.c

boards/airmind/mindpx-v2/src/spi.c

boards/atmel/same70xplained/src/init.c

boards/auav/x21/src/init.c

boards/auav/x21/src/spi.c

boards/av/x-v1/src/spi.c

boards/bitcraze/crazyflie/src/init.c

boards/bitcraze/crazyflie/src/spi.c

boards/emlid/navio2/navio_adc/navio_adc.cpp

boards/emlid/navio2/navio_rgbled/navio_rgbled.cpp

boards/emlid/navio2/navio_sysfs_rc_in/navio_sysfs_rc_in.cpp

boards/gumstix/aerocore2/src/init.c

boards/gumstix/aerocore2/src/spi.c

boards/intel/aerofc-v1/src/init.c

boards/nxp/fmuk66-v3/src/init.c

boards/nxp/fmuk66-v3/src/sdhc.c

boards/nxp/fmuk66-v3/src/spi.c

boards/omnibus/f4sd/src/init.c

boards/omnibus/f4sd/src/spi.c

boards/parrot/bebop/flow/bebop_flow.cpp