[InstCombine] Remove unreachable code for turning an And where all demanded...

[InstCombine] Remove unreachable code for turning an And where all demanded bits on both sides are known to be zero into a constant 0.

We already handled a superset check that included the known ones too and folded to a constant that may include ones. But it can also handle the case of no ones.

llvm-svn: 300093