cmake: drop duplicate inclusion of Custom.cmake
cmake: drop duplicate inclusion of Custom.cmake

Fixes #698

ketchupok/csound,ketchupok/csound,csound/csound,csound/csound,ketchupok/csound,ketchupok/csound,ketchupok/csound,csound/csound,ketchupok/csound,ketchupok/csound,csound/csound,csound/csound,csound/csound,csound/csound,csound/csound,csound/csound,ketchupok/csound,ketchupok/csound,csound/csound,ketchupok/csound