MODE-2323 Removed the proxy layer and delta write functionality in Schematic

ModeShape's is no longer using Infinispan in ways where these pieces of functionality are useful.
Removing them should simplify the logic to represent more of what we're actually doing. See MODE-2323 for details.
do we need to pass the `cache` as a parameter ? 

This seems "suspect" to me for a couple of reasons:
* `FederatedSchematicEntry` doesn't use the cache at all for this method
* `SchematicEntryLiteral` creation is always "internal" from the code perspective and once a literal has been created it is also placed in the cache, so it will (should ?) always belong to the same cache.

Actually, there are a some methods inside `SchematicEntryLiteral` which create a new instance but are unused: `newInstance`, `copyForWrite`. Also, it seems some of the constructors are public when they should really be `protected` or `private`.  IMO SchematicEntryLitarals should never be created from the outside. They should always be created internally when interacting with document store/schematic db.