d3d11: always link with d3d11.dll

We only support up to date Windows 7 with some Direct3D11 support.
Direct3D 11.1 was added in Windows 7 Platform Update [1], aka KB2670838 [2].

The screen capture and MediaFoundation plugins won't work on Win7/2008
without the platform update.

[1] https://learn.microsoft.com/en-us/windows/win32/direct3darticles/platform-update-for-windows-7
[2] https://support.microsoft.com/kb/2670838