OpenGL2: Use an idea from ETXreal and separate world VBO into separate VBOs by shader.

code/renderergl2/tr_local.h

@@ -1334,9 +1334,6 @@ typedef struct {
 	int			numDecisionNodes;
 	mnode_t		*nodes;
 
-	VBO_t          *vbo;
-	IBO_t          *ibo;
-
 	int         numWorldSurfaces;
 
 	int			numsurfaces;