wined3d: Remove a redundant ActivateContext() call in IWineD3DSurfaceImpl_UnlockRect().

The various LoadLocation() handlers already take care of activating an
appropriate context.

dlls/wined3d/surface.c

@@ -1548,7 +1548,6 @@ static HRESULT WINAPI IWineD3DSurfaceImpl_UnlockRect(IWineD3DSurface *iface) {
         switch(wined3d_settings.rendertargetlock_mode) {
             case RTL_READTEX:
             case RTL_TEXTEX:
-                ActivateContext(myDevice, iface, CTXUSAGE_BLIT);
                 IWineD3DSurface_LoadLocation(iface, SFLAG_INTEXTURE, NULL /* partial texture loading not supported yet */);
                 /* drop through */