gallium/hud: fix a problem where objects are free'd while in use.

gallium/hud: fix a problem where objects are free'd while in use.

Instead of trying to maintain a reference counted list of valid HUD
objects, and freeing them accordingly, creating race conditions
between unanticipated multiple threads, simply accept they're
allocated once and never released until the process terminates.

They're a shared resource between multiple threads, so accept
they're always available for use.

Signed-off-by: Steven Toth <stoth@kernellabs.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>