[SLP]Improve reordering for the nodes beeing used in alternate vectorization.

No need to include the order of the scalars beeing used as part of the
alternate vectorization into account when trying to reorder the whole
graph. Such elements better to reorder in the following phase because
the subtree still ends up in shuffle.

Part of D116688, fixes the regression in D116690.

Differential Revision: https://reviews.llvm.org/D116740