samples: wpanusb: remove unnecessary condition for ccflags
samples: wpanusb: remove unnecessary condition for ccflags

The condition in src/Makefile is not necessary since the
net_private.h is always included from wpanusb.c and is not
dependent on the transceiver.

Change-Id: I07a0bf599f328bacb8c5677f20eb221a05f30866
Signed-off-by: Johann Fischer <b39b26e1812eb092eb217277792f3735321fa456@phytec.de>

mbolivar/zephyr,zephyriot/zephyr,GiulianoFranchetto/zephyr,fbsder/zephyr,mbolivar/zephyr,Vudentz/zephyr,fractalclone/zephyr-riscv,ldts/zephyr,nashif/zephyr,mbolivar/zephyr,ldts/zephyr,runchip/zephyr-cc3220,kraj/zephyr,fractalclone/zephyr-riscv,finikorg/zephyr,rsalveti/zephyr,holtmann/zephyr,explora26/zephyr,zephyriot/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,zephyriot/zephyr,kraj/zephyr,explora26/zephyr,fbsder/zephyr,aceofall/zephyr-iotos,kraj/zephyr,finikorg/zephyr,aceofall/zephyr-iotos,aceofall/zephyr-iotos,Vudentz/zephyr,fractalclone/zephyr-riscv,nashif/zephyr,finikorg/zephyr,runchip/zephyr-cc3220,fbsder/zephyr,holtmann/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,punitvara/zephyr,rsalveti/zephyr,aceofall/zephyr-iotos,galak/zephyr,rsalveti/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,mbolivar/zephyr,punitvara/zephyr,rsalveti/zephyr,kraj/zephyr,GiulianoFranchetto/zephyr,fbsder/zephyr,mbolivar/zephyr,holtmann/zephyr,zephyrproject-rtos/zephyr,zephyriot/zephyr,galak/zephyr,ldts/zephyr,runchip/zephyr-cc3220,explora26/zephyr,galak/zephyr,Vudentz/zephyr,runchip/zephyr-cc3220,finikorg/zephyr,fractalclone/zephyr-riscv,Vudentz/zephyr,explora26/zephyr,ldts/zephyr,punitvara/zephyr,Vudentz/zephyr,punitvara/zephyr,aceofall/zephyr-iotos,galak/zephyr,GiulianoFranchetto/zephyr,rsalveti/zephyr,fbsder/zephyr,punitvara/zephyr,fractalclone/zephyr-riscv,runchip/zephyr-cc3220,explora26/zephyr,zephyriot/zephyr,Vudentz/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,holtmann/zephyr,zephyrproject-rtos/zephyr,holtmann/zephyr,kraj/zephyr,GiulianoFranchetto/zephyr,nashif/zephyr,ldts/zephyr