GLTFOverrides creates ever-expanding vocache

Environment

Any featurettes

Description

Beq Janus notes: In the current implementation of the vocache, the generic extras file has no extras support in killObject and has no pruning/delete functionality at all. As such, the overrides map just grows forever. Is working on a PR.

See details in the tpv slack channel.

Test Plan

Visit a region that uses many GLTF Overrides
wait until the entire scene is loaded
wander around for several minutes letting objects with overrides come into and out of your view and draw distance

Expected Behavior
the .slec files found in the viewer's object cache should not be continuing to grow without bound

• found in ${HOME}/Library/Caches/SecondLife/objectcache/ on mac
• found in %LOCALAPPDATA%\SecondLife\objectcache\ on windows