Fix https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1073

Related to https://github.com/Awesome-Technologies/synapse-admin/issues/132

This reverts commit 1fb54a37cb.

Seems like it's been pulled or something. It used to exist, but not
anymore. Not sure what's going on.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1017

Related to
https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1010

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1010

It's an optional service, so we shouldn't bother most people with it.

This reverts commit f825c7c263.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1010

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/868

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/962

Also removes some duplicate table of contents entries in maintenance-synapse.md

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/963

This also simplifies Prerequisites, which is great.

It'd be nice if we were doing these checks in some optional manner
and reporting them as helpful messages (using
`matrix_playbook_runtime_results`), but that's more complicated.
I'd rather drop these checks completely.

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/683

ot -> to

- removed build_database_list.yml

This may be especially helpful to existing playbook users
who happen to find themselves installing Go-NEB later on.