Fix public links

Fixes #2973 RUNTIME_NOSETUPFS doesn't exist anymore and was doing nothing. Using tearDownFS() instead.

Backported: https://github.com/owncloud/core/commit/412f0962e75e64becb9fcf5ece3e877159537b69 to fix the issue in stable5.

@icewind1991 @schiesbn @Contex @Happyfeet01 @hepaly @gdsjerry