remove old makefile targets

Makefile

@@ -59,15 +59,6 @@ javascript: ${BUILDS}
 	@mkdir -p build/npm
 	@cp -v src/zenroom.js      build/npm/
 
-# build targets for windows (mingw32 cross compile on Linux)
-include ${pwd}/build/windows.mk
-
-# build targets for linux systems (also musl and android)
-include ${pwd}/build/linux.mk
-
-# build targets for apple systems (OSX and IOS)
-include ${pwd}/build/osx.mk
-
 # build docker images and releasing
 include ${pwd}/build/docker.mk