Cleanup: Remove outdated columns

[martinheppner]

Depending on https://github.com/orgs/bahnzumberg/projects/2/views/1?pane=issue&itemId=31349270 the columns "internal_status" and "connection_url", "return_url" in table fahrplan should be removed.
In table tours the column "children" and "internal_status" should be removed. If "publishing_date" is not used, remove it too.

[Falsal]

connection_url , return_url did not show up in api
internal_status : commented out in all instances (2 files)
children : commented out in all instances (4 files)
publishing_date : removed / commented out in 3 files

[Falsal]

@martinheppner :
sync.js : check function mergeToursWithFahrplan and cities const in line 607; cities is not being used, either delete it or use it somewhere inside the function .