[RF] Use `recursiveRedirectServers()` in NormalizationHelpers

In the `foldIntegrals()` function that reverses the unfolting of
normalization integrals in the computation graph, some custom logic was
used to redirect the servers. However, it caused some failures in the
ASAN builds because it accessed invalid memory.

This commit suggests to fix that by using the already existing
`RooAbsArg::recursiveRedirectServers()` function for the same logic.

Furthermore, in `unfoldIntegrals()`, clients outside the computation
graph are not considered for the server redirection, which also fixes
ASAN build failures.