This reverts commit 1387a13e1d.
This introduced performance regressions on AArch64, when the cost of a
vector GEP + extracts is offset by the benefits of vectorizing the rest
of the tree.
The test in llvm/test/Transforms/SLPVectorizer/AArch64/vector-getelementptr.ll
illustrates the issue. It was extracted from code that regressed a SPEC
benchmark by 15%.