d3d11videosink: Remove resizing window hack and unify resizing flow

d3d11videosink: Remove resizing window hack and unify resizing flow

In earlier implementation of d3d11videosink where no shader was implemented,
the aspect ratio and render size were adjusted by manipulating the backbuffer size
with unintuitive formula. Since now we do color conversion and resize using
shader, we can remove the hack.