Implement "canary" support using cookie

Set cookie env=x to access the x symlink (needs to be created
manually). Direct access to x is forbiden.

Unrelated cleanups:

• Removed profileinfo, no longer exists
• Added vendor to block list, nothing should be loaded directly from there

Bug: T247992
Change-Id: Ic65c59a05e90794ee740fe5e33148ed69d3d8ea7