Revert two changes for kopano-webapp-plugin-files

The state is very unclear and upstream provides confusing information.
For now revert both changes done for CVE-2019-16774 and mark it again as
undetermined.

Revert "Further update for CVE-2019-16774/kopano-webapp-plugin-files"

This reverts commit 1e673fc5.

Revert "Update information for CVE-2019-16774/kopano-webapp-plugin-files"

This reverts commit 5c047a14.