[SLP] Revert everything that has to do with memory access sorting.

[SLP] Revert everything that has to do with memory access sorting.

This reverts r293386, r294027, r294029 and r296411.

Turns out the SLP tree isn't actually a "tree" and we don't handle
accessing the same packet of loads in several different orders well,
causing miscompiles.

Revert until we can fix this properly.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@297493 91177308-0d34-0410-b5e6-96231b3b80d8