Revert "[SLP] Loop aware cost model/tree building"
This reverts commit 8963edb534e28d548d8381675bb18af1770c3041 to fix
miscompilations/compile time regressions, reported in https://github.com/llvm/llvm-project/pull/150450#issuecomment-4037224288, https://github.com/llvm/llvm-project/pull/150450#issuecomment-4037481719 and https://github.com/llvm/llvm-project/pull/150450#issuecomment-4038134121
