Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1627

Reverts b1b4ba501fdfaa, 90c9801c560b6, a3c84f78ca9c65a, ..

I haven't really traced it (yet), but on some servers, I'm observing
`ansible-playbook ... --tags=start` completing very slowly, waiting
to stop services. I can't reproduce this on all Matrix servers I manage.
I suspect that either the systemd version is to blame or that some
specific service is not responding well to some `docker kill/rm` command.

`ExecStop` seems to work great in all cases and it's what we've been
using for a very long time, so I'm reverting to that.

ExecStopPost should allow us to clean up (docker kill + docker rm)
even if the ExecStart (docker run ..) command failed, and not just after
a graceful service stop was initiated.

Source: https://www.freedesktop.org/software/systemd/man/systemd.service.html#ExecStopPost=

Ref: https://matrix.org/blog/2021/12/13/disclosure-buffer-overflow-in-libolm-and-matrix-js-sdk

Until now, we were leaving services "enabled"
(symlinks in /etc/systemd/system/multi-user.target.wants/).

We clean these up now. Broken symlinks may still exist in older
installations that enabled/disabled services. We're not taking care
to fix these up. It's just a cosmetic defect anyway.

We were applying the low-memory system patch to webpack.config.js
on systems with < 4GB memory.

From now on, we also let people force-enable patching by toggling the
`matrix_client_element_container_image_self_build_low_memory_system_patch_enabled`
variable.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1357

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1357

Should have been done in 63f5a88fa0.

https://github.com/vector-im/element-web/releases/tag/v1.9.3

See:
- https://github.com/vector-im/element-web/releases/tag/v1.8.4
- https://matrix.org/blog/2021/09/10/pre-disclosure-upcoming-critical-fix-for-several-popular-matrix-clients

Element web/desktop has just been updated to fix some regressions in regard to VoIP.

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/1108

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1070

Related discussion here: 1ab507349c (commitcomment-51108407)

Fixes https://github.com/spantaleev/matrix-docker-ansible-deploy/issues/1070

Signed-off-by: Ahmad Haghighi <haghighi@fedoraproject.org>