Fix missing meetings in committee export

[Elblinator]

Current behaviour:
If a committee is exported then only one of all committee meetings is exported

Reproduction:

1. create a committee with at least two meetings
2. navigate to the committee-list view
3. export as CSV
4. only one meeting is listed in tn export

Wanted behaviour:
If a committee has several meetings then all meetings should be exported in the committee export

[reiterl]

This issue is at the moment not a good idea.

[rrenkert]

As decided in #3476 (comment) we can close here.