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/cea56df59ec4530d78e66fd341738d77e0ab1745 to fix the issue in stable5.

@icewind1991 @schiesbn @Contex @Happyfeet01 @hepaly @gdsjerry