Revert "[SLP]Initial support for reshuffling of non-starting buildvector/gather nodes."

This caused verifier errors:

  Instruction does not dominate all uses!
    %8 = insertelement <2 x i64> %7, i64 %pgocount1330, i64 1
    %15 = shufflevector <2 x i64> %8, <2 x i64> poison, <2 x i32> <i32 1, i32 1>
  in function ?NearestInclusiveAncestorAssignedToSlot@SlotScopedTraversal@blink@@SAPAVElement@2@ABV32@@Z

(or register allocator crash when the verifier was disabled).

See comment on the code review.

> Previously only the very first gather/buildvector node might be probed for reshuffling of other nodes.
> But the compiler may do the same for other gather/buildvector nodes too, just need to check the
> dependency and postpone the emission of the dependent nodes, if the origin nodes were not emitted yet.
>
> Part of D110978
>
> Differential Revision: https://reviews.llvm.org/D144958

This reverts commit a611b3f3.
It also reverts 7a4061ae which depended on the above.