Disable the user-download abstraction and corresponding addition, by default.

Disable the user-download abstraction and corresponding addition, by default.

This partially reverts changes introduced in commit 04b24660, without any
explanation. Those changes actually allow TBB to read e.g.
`@{HOME}/[a-zA-Z0-9]*`, that is most of users' personal files, which defeats in
great part the purpose of this profile. Likewise for read access to `@{HOME}/`,
which quite often contain folders whose name users might not want to leak.

Still, some people might want to use this, so let's leave these rules in here,
but commented out, explaining what the consequences of enabling them are.