[osx] - fixed XBMCHelper was never updated

This PR 
1. removes the binary XBMCHelper from our tree
2. ensures that XBMCHelper is built into the former directory of that stale binary
3. Changes the code so that the XBMCHelper service is installed/uninstalled as soon as the user enables the "start xbmc via remote" option - this is needed as manual migration path for users which had this option enabled in gotham and update to kodi (the path to the service binary is changed / corrected during the toggle)

Well remote control service on osx is broken since the rebrand because the rebranded code was never in effect due to the stale binary in our tree ;)

Solution was verified working by the user who found the broken behavior (which essentially was that xbmc couldn't be started anymore via remote)