Apparently, the function `texinfo-outline-level' was added to texinfo.el
in 1996 (ChangeLog.6) and removed in 2003 (ChangeLog.10).  In release
9.4f (1996) `outline-level' was set to this then newly added function,
which has been void for 19 years now.

I just noticed it now, because consult[0] checks if `outline-level' is
bound, in which case it is funcall'ed.  In .texi buffer with auctex
loaded, this triggers an error.  For that reason I'd appreciate it if
this patch could be applied: