fix: Removed .AsSingleQuery from EndUser Search query (#1707)

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## Description

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Removed .AsSingleQuery from EndUser Search query.

Tested locally with 50 million dialogs. Results show that the removal of
.AsSingleQuery() brings Enduser Search query performance up to par with
that of ServiceOwner Search. We should seek further improvements as
well, as query scaling seems to be an issue.

## Related Issue(s)

- #1706 

## Verification

- [x] **Your** code builds clean without any errors or warnings
- [x] Manual testing done (required)
- [ ] Relevant automated test added (if you find this hard, leave it and
we'll help out)

## Documentation

- [ ] Documentation is updated (either in `docs`-directory, Altinnpedia
or a separate linked PR in
[altinn-studio-docs.](https://github.com/Altinn/altinn-studio-docs), if
applicable)

src/Digdir.Domain.Dialogporten.Application/Features/V1/EndUser/Dialogs/Queries/Search/SearchDialogQuery.cs

@@ -158,7 +158,6 @@ public async Task<SearchDialogResult> Handle(SearchDialogQuery request, Cancella
 
         var paginatedList = await _db.Dialogs
             .PrefilterAuthorizedDialogs(authorizedResources)
-            .AsSingleQuery()
             .AsNoTracking()
             .Include(x => x.Content)
             .ThenInclude(x => x.Value.Localizations)