Comment # 1 on bug 1039705 from Michael Chang

Do you really think listing your LFS as "unknown Linux distribution" is not a
bug in itself ?

The background is most people get nothing in returning of that "unknown Linux
distribution" test but only suffering very significant slow down .. that's
major reasoning why it was removed, plus the the test can be inaccurate, making
it hard to maintain. 

IMHO, the unknown Linux distribution should be handled by your own custom boot
config as you know best what what it is. The os-prober should only focus on
supported "known" one, hence we can know how to fix if any distro-specific
error occurs.