cmake: do not set CMAKE_SKIP_INSTALL_RULES to ON
cmake: do not set CMAKE_SKIP_INSTALL_RULES to ON

This CMakeLists.txt is added via add_subdirectory() to the app's
CMakeLists.txt. If the app-CMakeLists.txt has install() rules and
wants to use them, setting CMAKE_SKIP_INSTALL_RULES to ON breaks
the 'make install' call.

Not setting this variable does not harm zephyr because zephyr does
not use install().

Signed-off-by: Patrick Boettcher <e5ed5156b6f9b5cfea22ed93d1184c375a5b92a6@posteo.de>

Vudentz/zephyr,zephyriot/zephyr,Vudentz/zephyr,Vudentz/zephyr,kraj/zephyr,Vudentz/zephyr,zephyriot/zephyr,explora26/zephyr,zephyrproject-rtos/zephyr,mbolivar/zephyr,explora26/zephyr,Vudentz/zephyr,kraj/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,ldts/zephyr,mbolivar/zephyr,finikorg/zephyr,finikorg/zephyr,punitvara/zephyr,punitvara/zephyr,Vudentz/zephyr,punitvara/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,explora26/zephyr,explora26/zephyr,mbolivar/zephyr,finikorg/zephyr,zephyriot/zephyr,zephyrproject-rtos/zephyr,explora26/zephyr,mbolivar/zephyr,punitvara/zephyr,galak/zephyr,finikorg/zephyr,kraj/zephyr,mbolivar/zephyr,ldts/zephyr,nashif/zephyr,kraj/zephyr,zephyriot/zephyr,zephyrproject-rtos/zephyr,zephyriot/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,nashif/zephyr,galak/zephyr,GiulianoFranchetto/zephyr,punitvara/zephyr,nashif/zephyr,kraj/zephyr,ldts/zephyr,galak/zephyr,nashif/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr