Add missing export on compatibility method
Add missing export on compatibility method

The destroy method on SegmentIndex is needed for backward
compatiblity, so it should definitely be exported in v2.6, as it was
for v2.5.

Change-Id: Id29faea5ae1719f1ea9201808aa9ce674574afc7

shaka-project/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,tvoli/shaka-player