Disable Lockdown extension

Created by: lahwaacz

This restores public access to recent changes, page history etc. which was disabled in September 2019 due to misbehaving crawlers/attack - see commits f2c518d3 and 8595e8d6.

Let's hope that our robots.txt has been improved since then and the server load will not increase much. If it proves to be still a problem, this commit can be reverted and we will figure out better solution.