Remove CMAKE_CXX_COMPILER hack for ARM build

Output of "configure.cmd VSSolution" for trunk version:

Detected Visual Studio Environment VS14-arm
Creating directories in output-VS-arm
Preparing reactos...
– The C compiler identification is MSVC 19.0.23918.0
– Check for working C compiler using: Visual Studio 14 2015 ARM
– Check for working C compiler using: Visual Studio 14 2015 ARM – works
– Detecting C compiler ABI info
– Detecting C compiler ABI info - done
CMake Error at CMakeLists.txt:19 (project):
The CMAKE_CXX_COMPILER:

cl

is not a full path and was not found in the PATH.

– Configuring incomplete, errors occurred!
See also "D:/Project/reactos/output-VS-arm/CMakeFiles/CMakeOutput.log".
Configure script complete! Execute appropriate build commands (ex: ninja, make, nmake, etc...).

After remove the hack the configure.cmd runs correctly with Visual Studio 2015 Community