direct3d: Remove unnecessary render target support check. Direct3D 9 dictates that caps.NumSimultaneousRTs must always be at least 1, which is to say that Direct3D 9 level hardware must always support render targets. (caps.NumSimultaneousRTs is meant to show if you can draw to multiple render targets in a single draw call.) We had already hardcoded SDL_RENDERER_TARGETTEXTURE as available earlier in the function anyhow. Fixes #4781.