VideoBackend: remove unused config vars.

No point to keeping around variables which are always "true".
Merge pull request #235 from magumagu/videobackend-unused-config

VideoBackend: Remove unused config variables.
OpenGL config: clear backend_info.Adapters on init

Fixes a minor UI glitch where if you switch from Direct3D to OpenGL, the
OpenGL config page would appear to have an adapter choice available.
Merge pull request #264 from magumagu/opengl-clear-adapters

OpenGL: Clear backend_info.Adapters on initialization
VideoSoftware: remove const memory usage of DebugUtil
Merge pull request #135 from degasus/videosw_debugutil

VideoSoftware: Remove const memory usage of DebugUtil
Use vista threading primitives on Windows to fix DSP LLE on thread