There's no real way to recover these unless we want to start importing
rulesets into realm. And that seems counter productive. This can only
happen if users don't have the dll present any more, and it was removed
far before realm was tracking rulesets (else it would have an
`Available=0` entry in realm to match).
One of my pending work items for post-realm merge.
The lowest-level import task is no longer asynchronous, as we don't want
it to span multiple threads to allow easier interaction with realm.
Removing the `Task` spec simplifies a heap of usages.
Individual usages should decide whether they want to run the import
asynchronously, by either using an alternative override or spooling up a
thread themselves.
If the operation timed out on..
```csharp
throw new TimeoutException(@"Took too long to acquire lock");
```
..from an update thread, it would not restore the update context.
The next call would then fail on the assert that ensures a non-null
context in such cases.
Can add test coverage if required.