D3D: Replaced shader-based depth range remap with viewport

This fixes UI rendering in some games mentioned in https://code.google.com/p/dolphin-emu/issues/detail?id=7785

It's not clear why the vertex shader depth remap was introduced in the first place. It's not present in OGL back-end.
Are I_DEPTHPARAMS.xy used anymore at all? If not, do you also want to remove this consts?