Revert "Add capability to store and retrieve model attributes as BLOBs"

This reverts commit 7d5605b35d69edf74caa681b4e20522590a040b8.
 Add capability to store and retrieve model attributes as BLOBs

Some Model classes store fetched content that exceeds the VARCHAR size
limit.  Instead of storing this content in cache files, this content
will gradually be moved into the database.  Cache files which contents
have been so transferred are then unlink()ed.