[llvm] Revert "[SLP]Support revectorization of the previously vectorized scalars" (PR #134604)

[Alexander Kornienko via llvm-commits]

alexfh wrote:

> > This breaks Transforms/SLPVectorizer/X86/reordered-masked-loads.ll. Apparently, the test relies on some changes in #133091.
> 
> Will you wait for the fix then? Will try to land it soon

We have a number of failures related to SLP vectorizer - I'll be trying to reduce and root-cause them next. As usual, it would be better to revert to green and reland with the necessary fixes.

https://github.com/llvm/llvm-project/pull/134604