softpipe: Remove sp_video_context.c from SConscript.

sp_video_context.c was added to SConscript in commit
ed24e190 (pipe-video merge) but no file
of that name was added.

src/gallium/drivers/softpipe/SConscript

@@ -35,7 +35,6 @@ softpipe = env.ConvenienceLibrary(
 		'sp_tex_tile_cache.c',
 		'sp_texture.c',
 		'sp_tile_cache.c',
-		'sp_video_context.c',
 	])
 
 env.Alias('softpipe', softpipe)