"textfile" will be replaced by "text file"

Resolves: #54893
Releases: 6.2
Change-Id: Ic7ce106a016f242cc47c70539876ff9810954a9b
Reviewed-on: https://review.typo3.org/26736
Reviewed-by: Michiel Roos
Tested-by: Michiel Roos
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind