Don't cache visual data model v8 handles.

Don't cache visual data model v8 handles.

The external resource is reference counted and resused irregardless of
whether the handles are cached, and the reduction in the number of
handles allocated needs to be comes at the cost of keeping  persistent
handle which have a negative impact on garbage collection.

Change-Id: I92996faab08a0ff76d21e56dbdafdd7522882d2c
Reviewed-by: Chris Adams <christopher.adams@nokia.com>