st/dri: list __DRI2_FENCE extension only where needed

The extension should be present (if applicable) in the list returned by
getExtensions(). AFAICT no loader has ever looked for it in
__driDriverExtensions/__driDriverGetExtensions.

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>

src/gallium/state_trackers/dri/dri2.c

@@ -2251,7 +2251,6 @@ const __DRIextension *galliumdrm_driver_extensions[] = {
     &driImageDriverExtension.base,
     &driDRI2Extension.base,
     &gallium_config_options.base,
-    &dri2FenceExtension.base,
     NULL
 };