Add data_index to Exodus driver

data_index[0] represents the time step (t_index) if HasModeShapes=0
or ModeShape otherwise. This commit also removes an unused variable.

Change-Id: I08716d6c904aa18eb5b6163a6d394e3c47bcb138
FIX: remove warning declaration of ‘’ shadows a previous local

Change-Id: Iea6e6b0b30a21dfc532d5c89f193696d60f182a1
Merge topic 'exodus-15127' into master

d3ba9c77 FIX: remove warning declaration of ‘’ shadows a previous local
9c7135b9 Add data_index to Exodus driver