This reverts merge request !23229

This reverts merge request !23140

The disabling of Gitaly was basically stubbing `Feature.enabled?` call,
which was never triggered.

Currently, we assume a "last_version" always exists for a wiki page.
In production, this is not always true. So, guard uses of it with a
null check.

Cleanup code, and refactor tests that still use Rugged. After this, there should
be no Rugged code that access the instance's repositories on non-test
environments. There is still some rugged code for other tasks like the
repository import task, but since it doesn't access any repository storage path
it can stay.

Hooks were run for wikis, but given the internal API wasn't responding
failures happended, as seen on:
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/18693

Closes gitaly#958

Related to #39805

Part of gitlab-org/gitaly#639

Closes gitaly#673

The special characters of a wiki title are now escaped correctly.

Signed-off-by: NRémy Coutable <remy@rymai.me>

Remove superfluous lib: true, type: redis, service: true, models: true, services: true, no_db: true, api: true
Signed-off-by: NRémy Coutable <remy@rymai.me>

This reverts commit cb10b725c8929b8b4460f89c9d96c773af39ba6b.

* Add WikiPage#id method returning associated SHA for wiki page commit