intel: Drop the batchbuffer flush on glFramebufferRenderbuffer().

There should be nothing special about this call compared to other
callers of intel_draw_buffer().

src/mesa/drivers/dri/intel/intel_fbo.c

@@ -450,8 +450,6 @@ intel_framebuffer_renderbuffer(struct gl_context * ctx,
 {
    DBG("Intel FramebufferRenderbuffer %u %u\n", fb->Name, rb ? rb->Name : 0);
 
-   intel_flush(ctx);
-
    _mesa_framebuffer_renderbuffer(ctx, fb, attachment, rb);
    intel_draw_buffer(ctx);
 }