D3D: remove NV GetDimensions() workaround for image load/store. RWTexture2D only has the 2-param version of GetDimensions(), since it already refers to a single mip and layer. So this workaround just causes compile failures. Bug: angleproject:7121 Change-Id: I675eaf9ffadd75e186423a55bc9822e00432f89e Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3566218 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>