Revert D84264 "[SCCP] Directly remove non-feasible edges" &...

Revert D84264 "[SCCP] Directly remove non-feasible edges" & 5db5b4bc

It breaks stage-2 build. Clang crashed when compiling
llvm/lib/Target/Hexagon/HexagonFrameLowering.cpp

llvm/Support/GenericDomTree.h eraseNode: Node is not a leaf node