Removed unused code from vtkModelMetaData and vtkExodusModel

Exodus readers and writers no longer support packing and unpacking
of model meta data so I removed all of the unnecessary code.

Change-Id: Iae190a9d5ca7b10ab128728a60918602bf809ed1
COMP: Fixed compiler error - needed to remove functions from .h.

Change-Id: Ia8fb1aeddb10ddf4106549d5f01fbdd79eecf764
Merge topic 'clean-exodus-model' into master

ee55278c COMP: Fixed compiler error - needed to remove functions from .h.
790115cf Removed unused code from vtkModelMetaData and vtkExodusModel