Remove add libusual to vpath
Remove add libusual to vpath

This has confusing effects if the super-project has a file with the
same name as libusual.

Superprojects can still set this manually if desired, but if they use
find_modules.sh they wouldn't need it anyway.

markokr/libusual,markokr/libusual,markokr/libusual,markokr/libusual