Fix handling of deletion/removal of account/participant

[Elblinator]

Current situation:
If accounts are deleted at the same time as participants are removed then an Error is thrown and nobody is removed or deleted from a meeting

Reproduction:

1. create two meetings (B and C)
2. Put participant D in both meetings
3. Put participant E in meeting B
4. navigate to the participant-list of meeting B
5. start multiselect and remove/delete D and E
6. Error is thrown

Wanted behaviour:
it should be possible to remove and delete users at the same time

Comment from issue #2723
[...] The broken locks error already existed beforehand. The reason is that the request is being sent to the handle_request route instead of the handle_separately route like it should be. But here:

openslides-client/client/src/app/site/pages/meetings/pages/participants/services/common/participant-controller.service/participant-controller.service.ts

Line 233 in 36888d9

await this.delete(toDeleteUsers, true)

the parameter is correctly given and should also be correctly kept in the concat method, also I suppose that the error happens somewhere in there.[...]

Originally posted by @jsangmeister in #2723 (comment)