Replace render delegate's "pause render" with "stop render"

[sebastienblor]

Our render delegate is currently declaring that is supports pausing renders (with IsPauseSupported returning true), but this isn't actually correct. At the moment, arnold cannot pause & resume renders. We should instead return true in IsStopSupported and no longer declare anything for pauses.

[autodesk-oss-arnold-bot]

Issue synced internally to ARNOLD-15791