st/mesa: remove unnecessary flushes

The framebuffer cache flush should be implicit when calling
set_framebuffer_state.

There is no need to flush the command stream either.

src/gallium/auxiliary/util/u_gen_mipmap.c

@@ -1660,8 +1660,6 @@ util_gen_mipmap(struct gen_mipmap_state *ctx,
                                  4,  /* verts */
                                  2); /* attribs/vert */
 
-         pipe->flush(pipe, PIPE_FLUSH_RENDER_CACHE, NULL);
-
          /* need to signal that the texture has changed _after_ rendering to it */
          pipe_surface_reference( &surf, NULL );
       }

src/mesa/state_tracker/st_cb_fbo.c

@@ -431,14 +431,11 @@ static void
 st_finish_render_texture(struct gl_context *ctx,
                          struct gl_renderbuffer_attachment *att)
 {
-   struct st_context *st = st_context(ctx);
    struct st_renderbuffer *strb = st_renderbuffer(att->Renderbuffer);
 
    if (!strb)
       return;
 
-   st_flush(st, PIPE_FLUSH_RENDER_CACHE, NULL);
-
    strb->rtt = NULL;
 
    /*