Revert "snapshot: Add virDomainSnapshotObjListParse"

Revert "snapshot: Add virDomainSnapshotObjListParse"

This reverts commit 1b57269cbcfcfe998a065c0c9f0f8db408710d87, and
subsequent refactorings of the function into new files.  There are no
callers of this function - I had originally proposed it for
implementing a new bulk snapshot API, but that proved to be too
invasive given RPC limits. I also tried using it for streamlining how
the qemu driver stores snapshot state across libvirtd restarts
internally, but in the end, the risks of a new internal format
outweighed the benefits of one file per snapshot.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>