[BUGFIX] Old files of filelist extension are wrong

During the namespace change the old filelist extenion files
are not correctly set. Instead of "filelist" this was replaced
with "file_list".

Fixes: #46155
Related: #45143
Releases: 6.0

Change-Id: I33ebb12163dd30d35981f45dcd465f7340bf1f5a
Reviewed-on: https://review.typo3.org/18845
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn