vrend: free unclaimed resources when context is destroyed
vrend_renderer_pipe_resource_create creates a resource that is then usually claimed with a call vrend_get_blob_pipe. However, if not all resources created like this are claimed then the memory used to allocate these has to be freed when the context is destroyed to avoid a memory leak.
Closes: https://gitlab.freedesktop.org/virgl/virglrenderer/-/issues/513