OCI: avoid spatial index to be created each time SyncToDisk() is called; remove unused OGROCITableLayer::FinalizeNewLayer(); avoid crash at ogr_oci.py termination

git-svn-id: https://svn.osgeo.org/gdal/trunk/gdal@27828 f0d54148-0727-0410-94bb-9a71ac55c965