Revert "[MLIR][Transforms] Fix Mem2Reg removal order to respect dominance (#68687)" (#68732)

This commit causes the following issue with sanitizers:

`include/c++/v1/__debug_utils/strict_weak_ordering_check.h:52: assertion
!__comp(*(__first + __b), *(__first + __a)) failed: Your comparator is
not a valid strict-weak ordering`

probably due to an invalid sort().

Revert "[MLIR][Transforms] Fix Mem2Reg removal order to respect
dominance (#68687)"

This reverts commit be81f42b.