nir/tests: Update the CF tests to not assume fake edges
nir/tests: Update the CF tests to not assume fake edges

In aad4f1550, we removed the concept of "fake" edges from NIR.  Now, if you
have a block at the end of an infinite loop it really has no predecessors.
This updates the unit tests to match.

Signed-off-by: Jason Ekstrand <68c46a606457643eab92053c1c05574abb26f861@jlekstrand.net>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97587
Tested-by: Aaron Watry <af2ebef3721cdd7b625ae5c26be8f78487857230@gmail.com>
Reviewed-by: Connor Abbott <71178acffcc112b21e5858656e5751f5e4aa9364@gmail.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler