st/dri: remove unused dummyContext value

src/gallium/state_trackers/dri/dri_context.c

@@ -109,9 +109,6 @@ dri_destroy_context(__DRIcontextPrivate * cPriv)
     */
    st_flush(ctx->st, 0, NULL);
 
-   if (screen->dummyContext == ctx)
-      screen->dummyContext = NULL;
-
    /* Also frees ctx->pipe?
     */
    st_destroy_context(ctx->st);
@@ -153,11 +150,6 @@ dri_make_current(__DRIcontextPrivate * cPriv,
 
       ++ctx->bind_count;
 
-      /* This is for situations in which we need a rendering context but
-       * there may not be any currently bound.
-       */
-      screen->dummyContext = ctx;
-
       if (ctx->dPriv != driDrawPriv) {
 	 ctx->dPriv = driDrawPriv;
 	 ctx->d_stamp = driDrawPriv->lastStamp - 1;

src/gallium/state_trackers/dri/dri_screen.h

@@ -49,12 +49,6 @@ struct dri_screen
     */
    driOptionCache optionCache;
 
-   /**
-    * Temporary(?) context to use for SwapBuffers or other situations in
-    * which we need a rendering context, but none is currently bound.
-    */
-   struct dri_context *dummyContext;
-
    /* drm */
    int fd;
    drmLock *drmLock;