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.
I think it's likely in a setup where data is inserted only offline (i.e. off another, "small" process) while the repository is mainly used for reading/writing.
The only thing relevant from the ISPN docs around this flag is:
```
boolean lock(K... keys);
@return true if the lock acquisition attempt was successful for <i>all</i> keys;
 * false will only be returned if the lock acquisition timed out and the
 * operation has been called with {@link Flag#FAIL_SILENTLY}.  boolean lock(K... keys);
```

so it would seem this flag is only relevant for timeouts.
However, the previous (to this PR) schematic code did a couple of interesting things with regards to locking:
in SchematicEntryProxy#getDeltaValueForWrite()
```
   // Otherwise, acquire the write lock ...
   boolean suppressLocks = flagContainer != null && flagContainer.hasFlag(Flag.SKIP_LOCKING);
   if (!suppressLocks && flagContainer != null) flagContainer.setFlags(Flag.FORCE_WRITE_LOCK);
```
which means that we are forcing locks (for some reason) if the mode is `PESSIMISTIC`
and
```
if (context.isExplicitLockingEnabled()) {
  context.getCacheForLocking().lock(key); // released at TXN commit/rollback
}
```
which means that we do support `OPTIMISTIC` as well.