The snapshots at the moment of search were held as long as the
corresponding search result panel was kept, to allow mapping of the old
symbol to the corresponding symbol in the new snapshot.
Now we just save the file name and ID of the old symbol.

Change-Id: Iaf3c9ca27ec2b788f142bd0dd6b86e34e66d5c8b
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>