We missed a few backwards compatibility functions in libexec/functions when removing SysV support back on bug 4290. These are just dead code now.
Removed the old functions and couldn't find any trace of them elsewhere in the tree.
I verified the claim in comment 2 and I could not find any traces of these functions. On top of this, I verified that previous users of the removed functions (`tl-run-xstartup.d` and tl-single-app`) still works as expected.