McuSupportPlugin: replace McuSupportCmakeMapper

Due to time pressure, we implemented McuSupportCmakeMapper as a quick hack to map the old Environment variables to the new CMake variables, hardcoding the mapping into the plugin.  It did the job at the time, but it was meant to be a temporary solution.

Once the issues with the hardcoded Environment Variables mentioned in the other sub-tasks of this epic are solved and we are properly parsing the information from the json files and using it to generate the needed CMake variables, this last sub-task is to remove that class.