Change the indexing of HyperTree and remove dead code & vars.
HT are now indexed in such a way that there is no more dead index. HTGSource in quadric mode use the GlobalIndexStart mode to avoid the storage of the local to global node id per tree (contrary to descriptor/mask sources which use a BSF global indexing mode, quadric nodes are numberered on a per-tree basis). Also remove some no more used functions and vars. Change-Id: Ie5fe5f267a22706334d883d330b8aa9bbb3926e2