Delete copies of the DirectX SDK

Removing the instances of the DirectX 2 SDK found at 'QW\dxsdk' and
'WinQuake\dxsdk'.

The DirectX SDK isn't really a library that should distributed alongside
the project and the libraries should be included from the build machine.
It is still simple to find a copy of such an old version of the DirectX
SDK with a brief Google search.